I don’t know Lineage, bit if it’s similar to classic Android, have you checked in Settings > Network and Internet > mobile network (with your provider name under) > Advanced Settings > Preferred network type > if “2G only” is selected instead of “auto 2G/3G/4G” ?
Please note that these settings denominations may not be exact, as I am on classical Android 10, on FP3, and translating myself.
I’ve had the same when using two SIM-cards. Please note the phone can only support one network at 3G or 4G and the other will be at slow speed. In your settings (I believe under ‘SIM’) turn one SIM down to 2G and permit the other to do 4G.
I tried some of the advices, but none of them worked so far.
setting apn manually doesn’t solve it
setting one of the simms to 2G doesn’t help
What I realized only now is that the automatic set up for mobile data via sms, doesn’t do anything. I just get a 4 digit pin and afterwards an info that my phone will be set up after I installed or saved the settings I just received.
I would expect a pop up by the phones OS that asks me to install the settings, but that doesn’t occur. Also sending back the PIN only creates an error message by the provider.
it appears that the problem was solved without any action on my behalf. The only idea I have is that it had to do with the SIM provider chaning from 3G to 4G. I got a message from them, however I couldn’t imagine that switching to 4G was accompanied by 3G not working at all.
Thanks for your kind advice anyway! Looks like this forum is very alive!