Help Google Drive sync issues on OnePlus 5

My father owns a OnePlus 5 (on the latest OS available for the device.) For the last few months (even before he updated to Android 10), he's had problems uploading and syncing (via FolderSync) on Google Drive (also the latest version because of auto-update.) Intermittently whenever he would upload files on Google Drive, he'd see 'Waiting to Upload' on the files but they'd never upload. This problem has persisted on at least two Wi-Fi and two mobile network connections.

The odd thing is that the issue is specific only to a sub-folder within Drive. If he tries to upload to the main Drive directory, the upload happens instantly.

FolderSync works only if I manually sync it. Auto-sync whether instantaneous or every 15 minutes does not work.

I've done the following things to try to repair this issue:

  1. Force stopped the app and restarted my phone. (many times)

  2. Disabled uploading only while on Wi-Fi.

  3. Logged in and out of the app.

  4. Cleared app cache and data.

  5. Disabled (can't uninstall the app) and enabled the app.

  6. Cleared my mobile cache in OnePlus:

  7. Disable power-saving and data-optimization for the app.

  8. Granted all permissions to the app.
None of these things have worked or made the situation any better. I contacted Google Drive support and they said that if you can upload files without any issues then the problem is with the phone.

I contact OnePlus and the phone cache reset is what they advised. It didn't work and now they've asked me to go to a service centre which I don't want to because it is far away from my house.