Cache Uid's & dedupe rebuildCards.

src/main/java/mezz/jei/gui/overlay/collapsible/GuiCollapsibleGroups.java

@@ -118,15 +118,24 @@ private void rebuildCards() {
 			? (List<IIngredientListElement<?>>) (List) Internal.getIngredientFilter().getIngredientList("")
 			: Collections.emptyList();
 
+		// Precompute UIDs once for all ingredients.
+		String[] elementUids = new String[ingredientList.size()];
+		for (int i = 0; i < ingredientList.size(); i++) {
+			IIngredientListElement<?> e = ingredientList.get(i);
+			@SuppressWarnings({"unchecked", "rawtypes"})
+			String uid = ((mezz.jei.api.ingredients.IIngredientHelper) e.getIngredientHelper()).getUniqueId(e.getIngredient());
+			elementUids[i] = uid;
+		}
+
 		for (CollapsibleGroup group : allGroups) {
 			CollapsedGroupIngredient ingredient = group.getIngredient();
 			List<IIngredientListElement<?>> previewItems = new ArrayList<>();
 			int itemCount = 0;
-			for (IIngredientListElement<?> element : ingredientList) {
-				if (ingredient.matches(element)) {
+			for (int i = 0; i < ingredientList.size(); i++) {
+				if (ingredient.matchesUid(elementUids[i])) {
 					itemCount++;
 					if (previewItems.size() < PREVIEW_FETCH_MAX) {
-						previewItems.add(element);
+						previewItems.add(ingredientList.get(i));
 					}
 				}
 			}
@@ -584,14 +593,6 @@ private <T> void renderIngredientTooltip(IIngredientListElement<T> element, int
 		}
 	}
 
-	/**
-	 * Called when returning from the editor screen to refresh the card list.
-	 */
-	public void onEditorClosed() {
-		rebuildCards();
-		rebuildPageButtons();
-	}
-
 	private static class GroupCardEntry {
 		final String id;
 		final String displayName;

src/main/java/mezz/jei/gui/overlay/collapsible/GuiCustomGroupEditor.java

@@ -8,6 +8,7 @@
 import mezz.jei.gui.ingredients.IIngredientListElement;
 import mezz.jei.ingredients.IngredientFilter;
 import mezz.jei.ingredients.group.CollapsedGroupIngredient;
+import mezz.jei.ingredients.group.CollapsibleGroup;
 import mezz.jei.util.Translator;
 import net.minecraft.client.gui.GuiButton;
 import net.minecraft.client.gui.GuiScreen;
@@ -90,11 +91,14 @@ public class GuiCustomGroupEditor extends GuiScreen {
 	// Maps each right-panel element to its stored UID (exact or wildcard ending in ":*")
 	private final Map<IIngredientListElement<?>, String> selectedStackToStoredUid = new HashMap<>();
 
-	// Index of OTHER custom groups — used to tint items that already belong to a different group.
+	// Index of OTHER groups (any source: DEFAULT, MOD, CUSTOM) — used to tint items that already belong to a different group.
 	// Built once in initGui(); key = exact UID, value = list of display names.
 	private Map<String, List<String>> otherGroupExactUids = new HashMap<>();
 	// [prefix, displayName] pairs for wildcard entries in other groups
 	private List<String[]> otherGroupWildcardPrefixes = new ArrayList<>();
+	// Pre-computed set of UIDs (from filteredItems) that belong to another group — used for O(1)
+	// per-slot lookup in drawLeftGrid() instead of calling getOtherGroupNames() every frame.
+	private Set<String> otherGroupUidCache = new HashSet<>();
 
 	// Drag-select state
 	private boolean isDragging = false;
@@ -219,31 +223,51 @@ private boolean isUidSelected(String normalUid) {
 	}
 
 	/**
-	 * Builds a reverse index of all other custom groups for fast membership lookup
+	 * Builds a reverse index of all other groups (DEFAULT, MOD, and CUSTOM) for fast membership lookup.
 	 */
 	private void buildOtherGroupIndex() {
 		otherGroupExactUids.clear();
 		otherGroupWildcardPrefixes.clear();
-		CustomGroupsConfig cfg = Config.getCustomGroupsConfig();
-		if (cfg == null) return;
-		for (CustomGroupsConfig.CustomGroup g : cfg.getCustomGroups()) {
-			if (g.id.equals(group.id) || g.itemUids == null) continue;
-			String name = (g.displayName != null && !g.displayName.isEmpty()) ? g.displayName : g.id;
-			for (String uid : g.itemUids) {
+		otherGroupUidCache.clear();
+		Map<String, CollapsibleGroup> allGroups = Internal.getCollapsedGroupRegistry().getAllGroups();
+		for (Map.Entry<String, CollapsibleGroup> entry : allGroups.entrySet()) {
+			if (entry.getKey().equals(group.id)) continue;
+			CollapsedGroupIngredient ingredient = entry.getValue().getIngredient();
+			String name = ingredient.getDisplayName();
+			if (name == null || name.isEmpty()) name = entry.getKey();
+			for (String uid : ingredient.getUids()) {
 				if (uid.endsWith(":*")) {
 					otherGroupWildcardPrefixes.add(new String[]{uid.substring(0, uid.length() - 2), name});
 				} else {
 					otherGroupExactUids.computeIfAbsent(uid, k -> new ArrayList<>()).add(name);
 				}
 			}
 		}
+		rebuildOtherGroupUidCache();
 	}
 
-	/** Returns the names of other custom groups that contain the given normal UID, or an empty list. */
+	private void rebuildOtherGroupUidCache() {
+		otherGroupUidCache.clear();
+		for (IIngredientListElement element : filteredItems) {
+			String uid = getIngredientUid(element.getIngredient());
+			if (!otherGroupExactUids.isEmpty() && otherGroupExactUids.containsKey(uid)) {
+				otherGroupUidCache.add(uid);
+			} else {
+				for (String[] entry : otherGroupWildcardPrefixes) {
+					if (uid.startsWith(entry[0]) &&
+							(uid.length() == entry[0].length() || uid.charAt(entry[0].length()) == ':')) {
+						otherGroupUidCache.add(uid);
+						break;
+					}
+				}
+			}
+		}
+	}
 	private List<String> getOtherGroupNames(String normalUid) {
 		List<String> names = new ArrayList<>(otherGroupExactUids.getOrDefault(normalUid, Collections.emptyList()));
 		for (String[] entry : otherGroupWildcardPrefixes) {
-			if (normalUid.equals(entry[0]) || normalUid.startsWith(entry[0] + ":")) {
+			if (normalUid.startsWith(entry[0]) &&
+					(normalUid.length() == entry[0].length() || normalUid.charAt(entry[0].length()) == ':')) {
 				names.add(entry[1]);
 			}
 		}
@@ -345,6 +369,7 @@ private void updateFilteredItems() {
 		if (leftPage >= leftTotalPages) {
 			leftPage = leftTotalPages - 1;
 		}
+		rebuildOtherGroupUidCache();
 	}
 
 	private void updateSelectedStacks() {
@@ -443,7 +468,6 @@ private void saveAndClose() {
 				filter.notifyListenersOfChange();
 			}
 		}
-		parentScreen.onEditorClosed();
 		this.mc.displayGuiScreen(parentScreen);
 	}
 
@@ -560,7 +584,7 @@ private void drawLeftGrid(int mouseX, int mouseY) {
 
 			// Orange tint if this item belongs to another custom group
 			String uid = getIngredientUid(ingredient);
-			if (!getOtherGroupNames(uid).isEmpty()) {
+			if (otherGroupUidCache.contains(uid)) {
 				RenderHelper.disableStandardItemLighting();
 				GlStateManager.disableDepth();
 				GlStateManager.colorMask(true, true, true, false);

src/main/java/mezz/jei/ingredients/group/CollapsedGroupIngredient.java

@@ -43,6 +43,8 @@ public enum GroupSource {
 	private final GroupSource source;
 	private final List<IIngredientListElement<?>> filterElements;
 	private final Set<String> uids;
+	/** Pre-extracted from {@code uids}: the prefix before {@code :*} for each wildcard entry. */
+	private final List<String> wildcardPrefixes;
 	private final int backgroundColor;
 	private final int borderColor;
 
@@ -61,6 +63,17 @@ public CollapsedGroupIngredient(String id, String langKey, int backgroundColor,
 		this.filterElements = new ArrayList<>(uids.size());
 		this.backgroundColor = backgroundColor;
 		this.borderColor = borderColor;
+		// Pre-extract wildcard prefixes so matches() doesn't scan all UIDs on every call
+		List<String> wc = null;
+		for (String uid : uids) {
+			if (uid.endsWith(":*")) {
+				if (wc == null) {
+					wc = new ArrayList<>();
+				}
+				wc.add(uid.substring(0, uid.length() - 2));
+			}
+		}
+		this.wildcardPrefixes = wc != null ? Collections.unmodifiableList(wc) : Collections.emptyList();
 	}
 
 	public String getId() {
@@ -97,15 +110,21 @@ public void toggleExpanded() {
 
 	public boolean matches(IIngredientListElement element) {
 		String uid = element.getIngredientHelper().getUniqueId(element.getIngredient());
+		return matchesUid(uid);
+	}
+
+	/**
+	 * Matches against a pre-computed UID string.
+	 * Prefer this overload when checking many elements to avoid recomputing the UID per group.
+	 */
+	public boolean matchesUid(String uid) {
 		if (this.uids.contains(uid)) {
 			return true;
 		}
-		for (String stored : this.uids) {
-			if (stored.endsWith(":*")) {
-				String prefix = stored.substring(0, stored.length() - 2);
-				if (uid.equals(prefix) || uid.startsWith(prefix + ":")) {
-					return true;
-				}
+		for (String prefix : this.wildcardPrefixes) {
+			if (uid.startsWith(prefix) &&
+				(uid.length() == prefix.length() || uid.charAt(prefix.length()) == ':')) {
+				return true;
 			}
 		}
 		return false;