roaming does not work reliable

What application is this relating to?

• Calls
• Chatty
• Mobile Internet

What problem did you encounter

I'm based in Germany and have SIM-Card at a reseller/MVNO in the Deutsche Telekom network.
When I headed to Austria and Italy for holidays roaming did not properly work.

What is the actual behaviour?

In Austria roaming never worked.
I got roaming of 4G and SMS working in Italy at one point. But I couldn't reproduce it with different maneuvers (reboot, HKS, settings).

What is the expected behaviour?

Roaming in the EU should work smoothly.

Which version did you encounter the bug in?

The system was fully patched back then (begin of September 2022).

• modemmanager 1.18.6-1pureos2
• gnome-calls 43~beta.0-1pureos1
• chatty 0.6.7-1pureos1

What hardware are you running on?

Librem 5 Evergreen with BM818-E1 modem

Relevant logfiles

I'll head to France this week end. So if someone could tell me what logs I should collect, I could provide them.