I have had a Pepwave Max transit cat18 , worked perfect for about a year with a verizon sim card. could lock onto band 13 and 66 for my best speeds but the modem died and they sent a replacement. hooked to the exact same hardware that I previously had and it connects fine to 13 and 66 and gets good speeds but as soon as it senses any type of idle in the connection it drops 66. I have to reboot. I read through a good bit of the forum and I have tried several suggestions with no luck. so for now my work around is to keep a download going and it will stay locked to LTE-A. I limit my download to around 1MB I have played around with the health check settings, disabled, enabled and set it to ping and the shortest intervals it would allow to keep my connection active, doesn’t help. also tried every firmware, from 801 to current, didn’t help either.
I have the same issue with the same modem. I have have the issue for months. I have to constantly reboot the device.