I set up the router in Austria where it worked fine. The selection of the network operator was set to automatically. After sending the modem to UK, it was not able to go online again. Therefore, I selected a provider manually. The modem worked fine again. Afterwards I again switched back to automatic mode, which also works now. According to the log files, there was not a single action of the modem until I took action manually.
Are there any settings for triggering the search for a new provider?
Normally I would expect that the router do this by itself.