I have Used Hash Caches enabled, and the command used to display the column was
GetSizes NODESELECT MD5 USEHASHCACHE
However I've never seen the cache files before.
Note, this is in a virtual drive created by the 'pCloud' client, and the files are stored on pCloud. If I had to guess, I would suggest it doesn't support "alt streams" transparently, or at all.
That's a bug in the cloud storage software. It's treating NTFS ADS (Alternate Data Streams) as separate files. If it doesn't support ADS, it should fail the request to create them, not create them as standalone files.
You should report the issue to the people that make the cloud storage software.
I'm happy to do that, but given my experience with their "support", is there any setting in DOpus I could use to exclude it from using ADS while I wait for it to be fixed?