Could you please clarify, did you change any settings on the router when the devices stopped getting internet connection or did they just not work initially when you setup the device?
Furthermore please try the things that @Marcelo.Barros suggested, changing the PDP type to IPv4 could help. As well as checking the DHCP leases, is a good thing to do.
For troubleshooting purposes, we will require more sensitive information from your end, such as the troubleshoot file, which may contain passwords, public IP addresses, serial numbers, and such. To avoid leaking this information, we have sent you a form to fill out, which you will receive in your e-mail inbox that you have registered your account with in the forums. In the Ticket ID field of the form, please enter the ID of this thread, which is 15567.
We will need you to send us a troubleshoot file from the device privately, so
To get a troubleshoot file:
Log in to WebUI
Press on System → Maintenance → Troubleshoot
Scroll down to Troubleshoot section and press “Download”
To help us troubleshoot, we need to rule out a potential routing issue on the end devices. This can sometimes occur if a device has multiple network connections (like Wi-Fi and a VPN active at the same time).
Could you please run the appropriate command below on a computer connected to the router’s LAN or WLAN network?
On Windows: Open Command Prompt and run route -4 print
On macOS: Open Terminal and run netstat -nr -f inet
Please copy the entire output and send it to us in a private message.