As I wrote at Solus Forums, E3276 LTE Rotator isn't working in Solus. After comparing some Ubuntu and Solus logs I found out that modemmanager isn't doing its job, as you can see here.
However, after running
sudo systemctl start ModemManager
in Solus, the stick gets recognized instantly, and can be used like it should. So is there a flaw in the dbus activation used by Solus or why it doesn't work?