So eventually I investigated the problem (as it appears B4a is NOT tested with such exotic servers as Samba - so buyers beware) and so far discovered, that it uses varying send buffer size 1 or 4 MB, with Windows default being 512 kB - improper buffer size is often reason for such problems. I've req...

Have you ever completed the first full backup? Can you tell (from files names being processed) if B4a just wants to complete the first full backup, or just starts all over?

So, B4a is not able to recognize files that are already in the target, unless they were backed up before.
You can not catch up the mirror backup with files already in the target.

Unfortunately this is not working in all situations. Again I am stuck in some state, where I B4a does not properly synchronize catalog contents with what is actually in source/target. Again mailed support. B4a has issues with getting the Test/Repair options to work right - instead of checking what i...

Fast forward 4 years and I have an identical issue.
I've already sent a message to support.

I contacted B4a support and they provided an advice to uncheck the "Smart file scanning mode" in backup properties.
This seems to work and the backup is progressing.
Still, I would expect Repair to handle such situations better.

So all is well that ends well.

So, maybe a word how I got to this state. I set up a new backup target server (same name, shares etc.) and recreated all mirror backups (like the problematic one) simply by running Repair. In case of this one, I needed to terminate running backup. I did it by using Stop option or just by closing com...

Oh, and if you want me to run some queries on bkp - no problem.

It looks to me like for some reason B4a is not checking source when repairing/testing. It's like it thinks it has actual state of sources and compares this state with backup - I have not noticed refreshing source data when doing repairs. Anyway, just to let you know - I've lost confidence in B4a (ar...

This is not the first time I have similar issues with B4a, but this time after two days of struggling I have really enough. After repairing backup using all the options in turn, I got eventually some files marked as to be backed up at the next backup execution. But this does not happen. See attached...