I tried hooking a cheap router after the LTE modem and so far it seems to be working. So thanks for that suggestion! Fingers crossed the failover works as well as I haven't had a chance to test that yet.
So in case anyone else tries a similar design, to reiterate my setup is:
A wired connection from my main home router to the LTE Netgear LB2120 Modem into the WAN port. Then from the Lan port on the 2120 i go to a cheap Dlink router and then on to the antminer. I have the antminer set to DHCP (not static) with the auto assign DHCP tuned on in the settings of the cheap router. The 2120 is set to bridge mode and this seems to be working. So now when there's an internet outage the 2120 should auto switch to LTE and the antminers stay connected until the hardwired connection is back online and it will then switch back from LTE to the hardwired connection.
Thanks again everyone for the help. Cheers!