I just switched over to a Fairphone 6 two days ago. Since then, I have not been able to receive any messages in group chats. I’ve tried on the default message as well as Google Messages. Nothing helps. I can receive texts individually.
I think it may be related to RCS. It says RCS is connecting and never does. I feel like I’ve tried every guide out there and nothing works. I sent in a ticket to Fairphone Support, but I’m tired of all this. Please please help 
Including guide for checking APN settings?
FPOS, /e/OS, …OS?
Quick search
1. RCS registration is stuck. Your phone number may still be registered with RCS on your previous phone, preventing Google Messages from activating RCS properly on the Fairphone 6.
Step 1: Disconnect RCS from your old phone
If you still have your old phone, open Google Messages and turn off RCS under Settings → RCS chats.
If you no longer have it, use Google’s official RCS deactivation page to unregister your phone number.
Then restart the Fairphone 6 and try activating RCS in Google Messages. Be aware that disabling RCS can affect existing RCS group membership.
Yes, I believe so. I’ve checked stuff with APN, so I believe that’s what you’re talking about.
It’s running e/OS that was pre-installed.
So in addition to what @yvmuell has proposed, did you also ask on the Murena forum?
I’ve tried what @yvmuell suggested to no luck, unfortunately. I’ll ask on the forum, thank you!
If you switched from an iPhone iMessage may not have disconnected correctly. If your phone plan allowed RCS on iPhone this may also be why it refuses to register to RCS on the fairphone.
If you no longer have your iphone you can deregister your number here:
Did you get the problem solved?
I had the same problem with my Fairphone 6 - purchased it a week ago. After trying everything (APN, changing SIM card etc.), I turned out that my network provider doesn’t support group chat and MMS to/from Fairphone. Kind of crazy, but I changed to another provider, and now everything works!
Good luck 
Which carrier did you end up going with? I am considering an FP 6+ and want to make sure I get mine on the right one!
I am i Denmark and changed to YouSee.