OnePlus 3T Connection Issues

All,

My device was connecting fine but this stopped working now and I got this error instead:

Failed to get children from device: hr=2147753993 facility=4 error_code=8201 description: No description available.

Traceback (most recent call last):
File "site-packages\calibre\gui2\device.py", line 90, in run
File "site-packages\calibre\gui2\device.py", line 513, in _books
File "site-packages\calibre\devices\mtp\driver.py", line 217, in books
File "site-packages\calibre\devices\mtp\driver.py", line 189, in get_driveinfo
File "site-packages\calibre\devices\mtp\windows\driver.py", line 268, in filesystem_cache
WPDError: Failed to get children from device: hr=2147753993 facility=4 error_code=8201 description: No description available.

I have already read several threads in this forum and I could fix the issue before with the very valid advice from kovidgoyal and others - many thanks for that. But now I don't get it to work again even when I tried all the instructions:

1) Try rebooting both the device and your computer
2) If that does not work, find the files driveinfo.calibre and metadata.calibre on the device
and delete them (you can use Windows Explorer or a file manager on the device itself to do this)
3) Reset the device

When I look at the jobs queue I find that the app is showing on the status column the files/directories it finds and at some stage about 20 - 30 seconds into the scan it stops with the error. When I repeated it does not stop at the same file (I thought there is a corrupted on the phone).

As I am running out of ideas, did anyone experience the same issue and could fix it?

Thanks for any help.