SMS and Internet not working reliably despite the indicators

I use Mobian Trixie on the Librem 5. After a few minutes, most of the time, I stop receiving and sending SMS reliably and using Internet despite the connectivity indicators telling me that 4G is available. I use some workarounds, restaring some SystemD services about modem and network manager helps, performing a call too.

This is the information about my modem firmware: Manufacturer: BroadMobi Model: BM818-E1 Revision: M1.0.0_E1.0.0.2_A1.0.4

Disabling autosuspend doesn't solve this problem.

This thread mentions some attemps to work around this bug.

My Access Point Names settings are correct. Please note that this bug isn't reproducible on the Pinephone under Mobian Trixie with the very latest community firmware with the same settings.

The librem 5 is now the phone I use daily, can you give me some guidance to solve this problem?