1) Isolate the network
- Switch networks (Wi‑Fi ↔ 4G/5G).
- Disable VPN/proxy (or test with/without).
2) Isolate account/session
- Confirm the Microsoft account.
- Sign out/in.
3) Sync client checks
- Check if sync is paused.
- Restart OneDrive.
- Check disk space.
4) Sharing/permissions
- For third‑party links/files, request access from the owner.