iterating over subFolders in background

Hi I have next code:

   guard 
        let url = self.documentDirURL,
        let folder = try? Folder(path:url.path)
        else { return }

    DispatchQueue.global().async {
        folder.makeSubfolderSequence(recursive: true).forEach { folder in
            let list = folder.subfolders.filter({
                $0.extension == self.projectExtention && $0.nameExcludingExtension != self.excludeProject
            }).flatMap { $0.parent }
            urls += list
        }
    }

as you may see - it scans all subfolders for subfolders with specific extension excluding specific filename, and put their parent folders in a list.

But when I put it in a DispatchQueue.global().async {} block (as shown above) - it stops at

    while let parentReferenceRange = path.range(of: "../") {

line in method
func pathByFillingInParentReferences(for path: String, prependCurrentFolderPath: Bool = false) throws -> String {
with error: Thread 2: EXC_BAD_ACCESS (code=2, address=0x70000bf20ff0)

In a stack I see over 1000 calls of FileSystemIterator.next() , so I think it's a recursion.

What I did wrong and how to fix it?

Start with pathByFillingInParentReferences(for:prependCurrentFolderPath:) and FileSystemIterator.next(), then reproduce the recursive subfolder scan inside DispatchQueue.global().async. Inspect the stack around the ../ path handling and iterator traversal; done means the scan completes without EXC_BAD_ACCESS and the reported case is covered by a regression test.