Ah, my apologies - did not understand that you meant that in the first place. Will do.
Replace the FPOS you have at the moment with /e/ OS (now known as Murena). It’s what I run on my FP2.
On these mentions …
The Developer options in /e/OS (the name stays for now, by the way) have a “Mobile data always active” switch, the description of this switch is “Always keep mobile data active, even when Wi-Fi is active (for fast network switching)”.
I switched it off because it significantly saves battery this way for me, but perhaps this could help to not cut mobile data when going Wi-Fi?
I don’t know whether it’s implemented in other OSes, though.
thats available on all OSs I used so far and I think its enabled per default. I checked it on the FP2 with FPOS Apr build and had to enable developer options and it was on.
You might use TWRP for a full backup (well, internal memory is not part of normal TWRP backup, but there are workarounds) and try out if factory reset helps in your case. Then you can restore your system as before using TWRP restore. If it helped you can still decide if it’s worth setting up the phone completely new after a factory reset…
Or if it helped you could do the factory reset and use TitaniumBackup to restore all apps and data (temporary root is quite easy on a FP).
Yes, 4G is working normally since then.
It’s rather my wifi that is not working as well sometimes, but I think it was the case before.