Two things you can try to solve the issue.
1.) The APN is in the "Custom" option, if you select "Auto APN", the router will set up the SIM card configuration in the best way posible.
2.) The 4G connection is selected as "prefered" band.
So, if your ISP is having problems with the 4G frequencies, the router won`t be able to reach 3G or 2G connections.
Using in "Automatic", the router will change the bands according with the ISP disponibility.
Please try with these tips and if you solve the issue please tell us know.