Phone is intermittently switching to "Emergency Calls Only"

I had a Samsung Galaxy S20+.  It had worked properly until a month or two ago, when I noticed the phone would intermittently leave the T-Mobile network and only allow Emergency Calls.  I was unable to receive or make calls and texts during those periods, which could last for 20-30 minutes at a time.  Since I was due for an upgrade, I assumed that switching to a new phone would resolve the issue.  I got a Galaxy Z Flip5. 

I migrated my data over from the old phone using Smart Switch, and noticed that the problem was occurring on my new phone.  So I backed up everything on Samsung Cloud, performed a factory reset on the new phone, and restored the data (minus the settings, since I thought there might be a rogue setting causing this).  This did not resolve the issue.  I did another factory reset and deleted the e-sim, in the event that something in the SIM card was causing the issue.  I replaced it with a physical SIM.  No change. 

After the last factory reset, I restored everything from Samsung Cloud and then reset the mobile network settings.  No change.  I verified that there were no system updates available.  I disabled 2G on the phone, as the T-Mobile reps suggested there could be a conflict between 5G and 2G.  No change. 

In the access point names, I've verified that the APN is correct (fast.t-mobile.com - I'm in the US).  In the Network Operators section, it is set to Select Automatically.  I turned that off and attempted to register on T-Mobile, which works.  But after a while the phone goes back to only allowing emergency calls. 

This happens everywhere I go, so it doesn't appear to be signal issue.  My wife is not experiencing this issue with her phone, so it appears to be restricted to my phone/account in some way.  I'm at a loss as to how to proceed.