I experience the same issue since upgrading my FP3 to Android 13.
I live on the Swiss/French border and have a Swiss and a German SIM. Whenever I cross the border into France, both SIM cards switch to a French network relatively quickly, but then stay on that French network even if I return to Switzerland. This stays like this for days on end until I make a trip away from the border region where there is no French network available anymore. I can even restart the phone, remove and reinsert one or both of the SIM cards and in particular the Swiss SIM (from GoMo) will connect to the French network again. And the reception of the Swiss network is definitely better that the French one, where I live…
Before the Android upgrade I could easily switch off automatic network selection, choose the Swiss network and then re-enable automatic network selection. Now, after the upgrade, once my phone decides it likes the French network better, I cannot use mobile data (unless I enable roaming, which isn’t really affordable with my contract) until I either pick up my bike or buy a tram ticket and ride 3-5 km from the border. Pretty inconvenient, if you ask me.
Is there anything know about this behaviour? Do other people besides @legenderic and @thmslg experience this? Is this Fairphone specific or does it also occur on other phone with Android 13? I found googling this issue very difficult and didn’t really find any reports matching my experience. Is there any remedy?