try this

release/check-submodules.sh

@@ -11,10 +11,18 @@ while read hash submodule ref; do
   git -C $submodule remote set-url origin $REPO_URL
   git -C $submodule fetch --depth 100 origin $BRANCH_NAME
   git -C $submodule branch -r --contains $hash | grep "origin/$BRANCH_NAME"
-  if [ "$?" -eq 0 ]; then
-    echo "$submodule ok"
-  else
-    echo "$submodule: $hash is not on $BRANCH_NAME"
-    exit 1
+  if ! git -C $submodule branch -r --contains $hash | grep -q "origin/$BRANCH_NAME"; then
+    echo "$submodule: $hash is not on $BRANCH_NAME in fork. Falling back to main repo."
+
+    MAIN_SUBMODULE_URL="$MAIN_REPO_URL/$submodule"
+    git -C $submodule remote set-url main "$MAIN_SUBMODULE_URL"
+    git -C $submodule fetch --depth 100 main master
+
+    if ! git -C $submodule branch -r --contains $hash | grep -q "main/master"; then
+      echo "$submodule: $hash is not on $BRANCH_NAME or master in the main repo."
+      exit 1
+    fi
   fi
+
+  echo "$submodule ok"
 done <<< $(git submodule status --recursive)