All router connections dropping for few seconds

I have very strange issue with my router board RB2011UiAS-2HnD-IN.
Once in a while, it drops all connections (both input - winbox and forward) and there is nothing in the logs that suggest what the issue might be.
the CPU, Memory, temperature is ok, voltage stays at 24 volts…, the router is not restarting.

Any suggestions what to test ? I have been googling mirkotik random disconnects from the rooter, yet nothing that helps …
I got power surge before this started happening, can be this the cause ?