USG 60W internet connection drops

I have USG60W connected to outdoor Zyxel NR7101 modem/router (previously LTE7460 modem/router). I have been experiencing internet connection cut outs and it seems the only solution is to reboot the modem (the same problem with both modems). The Internet connection doesn’t come up by itself. I have contacted my ISP, but all is well on their end. I’m able to connect to the NR7101 with LTE Ally software on my cell phone when the internet connection is down and it shoes that the modem is connected to the internet. So that turns my attention to the USG60W. Any suggestions of what I should check? I have the latest 4.62 firmware.