Supermicro BMC watchdog-caused reboots
Solution 1:
Eventually, I found a little bit strange solution: just leave watchdog jumper (JWD1) open (with neither NMI nor hard-reset selected). Watchdog is enabled in BIOS settings.
In this case watchdog works as expected -- system was stable for 25 minutes with bmc-watchdog running and rebooted after watchdog program termination.