diff --git a/.changeset/fix-access-control-silent-error.md b/.changeset/fix-access-control-silent-error.md
new file mode 100644
index 00000000000..206a1c1ee32
--- /dev/null
+++ b/.changeset/fix-access-control-silent-error.md
@@ -0,0 +1,5 @@
+---
+"@keystone-6/core": patch
+---
+
+Fixed an issue where database errors (connection issues, timeouts, etc.) occurring during unique item existence checks (e.g. in relationship resolvers) were silently swallowed and replaced with a generic "Access denied" error. Unexpected errors are now correctly rethrown to aid debugging.
diff --git a/packages/core/src/lib/core/access-control.ts b/packages/core/src/lib/core/access-control.ts
index 88a488123c8..10a6448e2df 100644
--- a/packages/core/src/lib/core/access-control.ts
+++ b/packages/core/src/lib/core/access-control.ts
@@ -17,6 +17,7 @@ import type {
   ListFilterAccessControl,
   ListOperationAccessControl,
   UpdateListItemAccessControl,
+  DeleteListItemAccessControl,
 } from '../../types'
 import { coerceAndValidateForGraphQLInput } from '../coerceAndValidateForGraphQLInput'
 import { accessDeniedError, accessReturnError, extensionError, formatKeys } from './graphql-errors'
@@ -428,7 +429,15 @@ export async function checkUniqueItemExists(
   try {
     const item = await context.db[foreignList.listKey].findOne({ where: uniqueInput })
     if (item !== null) return uniqueWhere
-  } catch (err) {}
+  } catch (err: any) {
+    // If it's an access denied error from context.db, we swallow it and throw our own
+    // to keep the error message consistent with "item may not exist".
+    // But if it's a real database error (e.g. connection, timeout, malformed query),
+    // we MUST rethrow it so the developer knows what happened.
+    if (err?.extensions?.code !== 'KS_ACCESS_DENIED') {
+      throw err
+    }
+  }
 
   throw accessDeniedError(cannotForItem(operation, foreignList))
 }