Thank you, Daumantas,
I've tried to apply your advice and got the secondary modem working with a manually set APN and manually selected network. The primary modem isn't working at all, though, after many experiments.
What I did, step-by-step:
- first, in the morning I discovered that both modems were stuck. There were lots of "modem unresponsive" messages in the logs, so I tried to reboot the device. Soft reboot (via the Web UI) didn't seem to help - the secondary modem came to life, but the primary didn't. So I tried a hard reboot - unplugged the power cord, waited for a while, and plugged it back. Now primary modem has also started flashing its LEDs like it should;
- I tried setting APN manually as you recommended. It didn't help either of the modems to connect in "Auto" mode, despite APN settings being the same for two operators in this area (O2.cz and Vodafone.cz);
- then I tried to do a manual network search, and the secondary modem connected to O2 - hooray, some progress!
- the first modem was still unable to connect, though, even when I manually tried to select O2 or Vodafone networks. I noticed that both LEDs were blinking, indicating something was wrong. I tried to click the "Restart connection" button on the Status > Network > Mobile tab for the first modem and observed the "Modem not ready" error message;
- I tried to SSH to the device and execute the "mctl -r -m modem" command, which seemed to help with the "Modem not ready" message, I can now "Restart connection," and it doesn't throw an error. The modem wasn't connecting, though;
- I adjusted the APN setting for the primary modem for the third operator available in this area (T-mobile.cz) and tried manually connecting to it. The modem didn't connect and was blinking two LEDs all of the time, so I tried a hard reboot again. No luck; nothing changed after the reboot;
- so I tried to swap the SIM cards. I pulled the SIM card from the secondary modem and inserted it in the first slot, leaving the second slot empty for now. The modem tried connecting for a while and then started blinking both LEDs again. When I selected Network > Mobile > Mobile operators tab, I saw an error message saying, "The modem is busy, connecting to operator". It can perform operators scan, though. I set APN settings for O2.cz (which was working for this SIM card in the secondary modem) and tried selecting O2 manually. It was trying to connect for a while and then started blinking both LEDs again, so I did a hard reboot again. No luck; it still can't connect. I think I waited long enough - for 15+ minutes.
- then I was wondering if I could get the first SIM card working in the second slot. I can't. The APN settings were set for O2 / Vodafone, and it couldn't connect to either. Previously, I checked this SIM card on my phone, and it successfully connected to Vodafone.
Bottom line: I have two SIM cards and two modems, and the only combination that works is SIM card #2 inserted into the secondary modem, with manual APN settings and manual network selection. All other combinations don't work, even including the only working SIM card in the other slot with the same settings.
Could you please advise on how to proceed? I've attached another troubleshooting file to the original question.