How to fix Error Code 0

I regularly copy files onto external drive as I am always having to manage space on my Macbook internal drive. I have 2 external drives and both are formatted as Mac OS Extended (Journaled).

It has been fine in the past but now when I try to paste/merge folders I get an unexpected error code 0 on some (not all) folders, and on both external drives.

I have read about this error in copying large files but that is not the case here.

I can copy files and folders within the main folder but not the whole folder. And then when I try to copy the folder on extrnal drive 1 and paste on external drive 2, I get the same error code.

My OS is Macos Big Sur v11.7.4