FFS seems to cause the remote disk to become unavailable

[lvl1]

I have 2 pc's synchronising with the same harddisk which is attached to my router by USB. One pc works perfectly, on the other one I allmost never manage to synchronise.
I start with a compare. This works quick enough, with a maximum of a couple of seconds before it starts reading from the remote disk. At this moment the remote disk is perfectly accessible through FFS and through the windows explorer. Then I start examining the differences and resolving the conflicts. When starting the synchronisation, I first get the message that the lock file cannot be written, then the message access denied. At that point I don't have access to the disk anymore, also in the windows explorer.
The log is very sparse. Is there more information available somewhere?
Thanks.

[Zenju]

You can try to disable the lock file and see if this helps: https://freefilesync.org/manual.php?topic=expert-settings