I have solved my problem, so that ends the question.
First I moved my Syno server to a different subnet and one problem was solved, but the intermittent disappearance of the user directory as described here was still happening, so I moved my array to another server, TueNAS Core. Now the problems are gone and hopefully won't come back.
Now my unRAID only works for docker containers.
upd.
I shouldn't have hoped for anything. Some problems remained though. Several times I noticed that I could not access the web interface. If you leave it for a while, the control comes back.
Honestly - I'm getting tired of looking for solutions to problems, 6.13 is coming soon and new problems. The system should just work for me, but in this case I am working for it. I'm moving the main docker containers to other servers. UnRAID will be a test environment, I will wait for the developers to fix the bugs.
XiMA4's post in unRAID server freezes after the Synology NAS is turned on was marked as the answer