Network connection lost after long phone calls

[amers]

After about every other long(ish) phone call that lasts about 10 minutes or longer, my FP2 loses its connection to my providers. I’m not available to incoming calls then (as if airplane mode was on). On the FP2, the connection bars drop to zero for both SIM cards. (Primary SIM is Austrian network “bob (Roaming in A1)”, secondary SIM is Austrian network “A1”.)

Turning on and off airplane mode does not help. The only thing to get the phone going again for normal phone calls / mobile internet is to reboot it.

Has anyone else had similar experiences so far?
Any idea how to proceed (except from contacting support, which I might do at some point…)

[amers]

Update: that’s what my connection bars looked like today, just shortly after a call that lasted 22 minutes:

The primary SIM does not show any network reception bars, the secondary SIM also is not properly registered with the provider network (when calling its number from another phone, I ended up in my mailbox - after an unusual delay of about 10 seconds, that is, which makes me think that the FP2 did not sign off the network properly).

The phone runs Fairphone OS 17.09.3.

[AnotherElk]

Hmmm … I can imagine it is not the favourite choice to make long calls just for testing, but until better ideas appear …

Does this behaviour stay the same if you use either of the two SIM cards alone without the second one in the phone?

Does this behaviour stay the same if you switch the SIM card slots for the cards?

If there’s a possibility to test the SIM card(s) in another phone … does this behaviour move with the SIM card(s) to the other phone?

[amers]

I’ll give it a try, thanks. Yet, I have to get my hands on some spare phone somewhere, first, so that I can start calling it wildly

[amers]

I did several test calls over the weekend, with both SIMs, even at the very same location where the latest occurrence of the problem was a few days ago. Yet, I couldn’t reproduce the behaviour - not sure at the moment whether that’s or .

Is there a way to activate and/or check any system or network connection logs on the FP2, that might help to find out what goes wrong when the hiccup occurs?