We have a client with 100 bases M700 and 200 handsets M25.
The building is 10 floors.
The problem is with the calls quality because the handsets from 6th floor are connecting to bases from the 3rd or 4th floor.
But the 11 bases from 6th floor look working just fine.

Can you advise what could be the problem ?

The firmware version is 520 branch 1.
Should we update the firmware and is it RISK FREE ?
Is it RISK FREE also to use the button - "Reconfigure Dect Tree" when we have such issues ?