Hey @F_Barrenbach!
I’m not sure whether I have the same problem as you but I have the FP1 first badge and it crashes way too often since the 1.8.5 update.
In my case it doesn’t appear within calls. A crash occurres every now and then when I use the phone, for example while opening an app or settings, just looking at it or typing a text.
While I know that it’s not connected to the SIM-cards, I strongly suspect the battery to cause these issues because the display and a network connection consumes more power than other background activities on the phone.
Unfortunately the support and I couldn’t verify this hypothesis but could you find a solution?