After spending about 5 hours with Verizon Tier 2 Technical Support over the last several days, we finally got the SIM card working. They don't provision your RUTXxx's IMEI correctly in your plan by default, even if you've given it to them multiple times. You can see this by logging into your MyVerizon account via the browser (not the mobile app), and checking your "Device ID". Over the phone, they insisted it was correct, but when I logged in, it was wrong. They had to escalate and get a Supervisor on the call to override the setting.
That said, also by default all SMS is BLOCKED on data-only SIM cards. You have to specifically call them ask them to remove the SMS block on your SIM, in order to allow SMS to work, when provisioned against an IMEI that is a router. I had them do this today to my SIM, but I still can't send/receive SMS via the RUTX11. But popping that same SIM into a spare iPhone8, and I can send/receive SMS just fine.
The issue appears to be that there is no way to independently configure the SMS/MMS settings in the RUTX11's interface settings or mobile settings. I tried 11 different APNs, restarting the router between each change, and none of them allowed SMS to flow.
I can pop my T-Mobile SIM into either slot, and SMS works just fine with that carrier. Just not with Verizon's SIM card. Oddly, there's no way to tell the RUTX11 that SIM2 handles SMS, but SIM1 is the default, or even load-balanced between the two.
So I'm in a similar boat; Verizon SIM now works (minus displaying the "Cell ID", which my T-Mobile card shows), and no SMS. I'll keep hacking on this until I figure it out, and post back here with results.