Failed backup: Writing directory metadata failed

hello all. This is my first post here. First off i would like to thank you all for this very nice program URBackup is.

Some info about my issue:
I have backups running on 4 machines (2x windows 10, 2x Debian 10) . The Windows clients are running without issues. But on the Debian machines i get following error:

Writing directory metadata to “/backuppc/hans-pc/201203-1116/.hashes/hans/.config/KeepSolid Inc./.dir_metadata” failed.

and warnings like these:

Error setting file time of /backuppc/hans-pc/201203-1116/hans/.Scilab/scilab-6.0.1/scinotesConfiguration.xml . Operation not permitted (code: 1)

The server is running on a RPI-3B (not ideal maybe, but it gets the job done). The storage is on a Qnap nas drive mounted to the RPI.
It gets mounted with the following line in my fstab file:

//“NAS-ip”/backuppc /backuppc cifs username=$$$,password=$$$,dir_mode=0777,file_mode=0777,_netdev,uid=110,mfsymlinks,vers=2.0,gid=116 0 0

Both Debian machines have this keepsolid folder. Inside this folder is only 1 vpn-config file (with my limited Linux knowledge i don’t see anything strange to this file/folder).
For now i have excluded this folder from the backup and at the moment i’m running a new full backup, up untill now i dont have any errors.

Can one of you guys and girls point me in the right direction to solve this problem?

Some minor thing i find strange:
When a backup fails it doesnt show at the front page of the server gui. It still points to my first ‘test’-backup (with a small folder), and gives a green OK sign.