lb2120 configuration issues

Trying to get this LB2120 to work.  When I connect the wan of the lb2120 to cable router ethernet port, and the lan side directly to computer, I get internet and can navigate pages. (it is in bridge mode and connection is from the landline.) When I unplug the wan port cable the modem connects to the cellular network, however, I cannot navigate to any pages.  Windows trouble shooter says there is a connection and cannot find any issue.  The lb2120 shows a lte/4g connection.  If I then reinsert the wan cable, the modem falls backover to the wired connection, but I cannot navigate pages and have to reboot my cable modem to restore function.

If I, instead connect the lan port to a router, there is no page navigation either wired or unwired.

The lb2120 GUI shows that there are no updates available, all are current. Have spent many hours diddilying with this thing.

T-mobile is provider.

Any help would be appreciated as support is awol.