Maybe something wrong with serial 5 on cons port

Hello, i am using serial 5 on cons port on a pixhawk 2.1, it works but out of 5 starts the flight controller hangs up a couple of times on startup.

Is there anything i have to do to use cons port on serial 5 apart the usual settings on the serial itself?

Just to make it clear, whaen the unit starts the serial works and telemetry data flow to my frsky telemetry on that port but on startup the unit sometimes (about 2 hangs up every 5 starts) locks up and motors keep beeping.