sessionfile not working

[bc-networks]

using version 1.2.5 with sdk 6.5.0 build-4566394 on debian11 (bullseye).
After deleting session files in /tmp, new file is generated after first check, and all looks fine. But with second check, it fails with <Timeout exceeded.>UNKNOWN: Script killed by monitor.
Deleting the sessionfile a second time, same procedure. Using --nosession always works, but should not be best practice.
Any idea wheather to find the problem?

thanks