Yep. Reading this thread I was thinking: old, old problem. It's one of the reasons I can't aways use this phone as a primary. I assume it has something to do with U.S. networks and Jolla indifference since they don't sell their OS here. Same with the inability to participate in group texting. It's really short-sighted to ignore these basic features, even if Europeans seem not to care about them.
Anyway, it's a habit now for me to use the option in Utilities to restart the network subsystem whenever I turn off wifi because I know it broke the ability to do MMS.