SERVO DRIVES GOING OFF

Hello all,

I have a CNC machine from CMS - MAXIMA BERBANA 5AXIS and today all of sudden the servo drives going off.
You can see the media I uploaded that the problem is overload on z-axis, when the value is going over 300% the servo drives closing.
Only in the first time this error appeared 436 Z axis: soft thermal (ovc) alarm, and never again.

Can you please point me the right direction where to start? or what is the possible problem?

https://www.youtube.com/watch?v=qpdkx0zUoig

Thank you in advance!