Not receiving group messages on GS9 - "null" message from 111301000

I am able to send messages in group text threads but any replies are coming in from phone number 111301000 with a "null" messages. This just started happening - I've been able to send/receive since getting the phone 2 weeks ago. Was using Textra app - switched to Samsung messages app and same result. I've messed with texting settings and powered phone off/on. Driving me crazy! Help!

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