It happens from time to time that somebody calls me and after 5 seconds my phone freezes. I have to hold power button for long time and my phone restarts. It happened to me a while ago with the new version 1.8 and many times earlier with 1.6. I use 2 sim cards, it doesn’t matter what sim card is used during that phone call.
This is a weird bug, I’ve never seen before. Maybe you should open a support ticket for one-on-one support with the Fairphone team as I haven’t seen this before 
Hi, any information on this yet? I have the same problem.
To be more specific - I noticed it is happening only if a bluetooth headphones are connected.
These are really uncommon issues. I’d suggest contacting support. (If the problem still exists of course, since I’m 5 months late 
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