Hi @thijs.notable,
This does seem to be odd behavior. Can I check, do you have a Health-Check enabled ? Whilst everyone has they preferred check, I like the DNS lookup :-
I would try setting the Offshore SIM as the preferred SIM, as this only has one network it can connect to, whereas the Onshore SIM has data roaming enabled, so it is likely to keep searching for networks. If you know the Country codes that the Onshore SIM is likely to connect to, this may also help - it is possible this SIM is trying to connect to the offshore network and failing the authentication, if you leave it as “All Countries”:-
You may want to adjust the Idle Timeout to something more suitable for your needs.
Here is a link to another Forum Post with a bit more information about the Country Codes and a link at the bottom to find the codes, etc > Here <
Hope this helps,
Steve