PixHawk sometimes arm sometimes not


When i press the safety switch it sometimes makes a sound and goes to solid blue. In this cases when i arm the motors start to spin and everything seems ok.

In other times the safety switch only turns to solid blue (from blink) with no sound and if i arm i hear that arm sound but the motors don’t spin. IF i press the safety switch again it sounds to lock.

I have made it connected to mission planner and no error msgs appear. The armed msg appears in both cases.

Do you have an idea of what is going on?

Thank you

What ArduPilot firmware are you using.
Also, please provide tlogs and/or dataflash logs to help troubleshoot your issue.