Modem or SIM gets clogged with old SMS, blocking processing of new SMS

I had a situation on June 7 where my Pinephone was suddenly unable to receive any SMS messages while it had my Verizon SIM. It could receive SMS with my Ting/T-Mobile SIM. I could send SMS with eiter. I eventually found the "AT+CMGL=4" command and saw the modem was apparently "clogged" with 99 messages - some from 4 months earlier when I sent my first SMS (I have preserved this output). A weird thing is that with the Ting SIM, "AT+CMGL=4" returned an empty response. It suggests these messages are actually stored on the SIM or perhaps the modem has seperate storage for each SIM it has seen?

Here are the reponses from AT+CPMS? for the 2 SIMs: Ting/T-Mobile: '+CPMS: "ME",0,23,"MT",0,23,"MT",0,23' Verizon: '+CPMS: "ME",99,99,"MT",99,99,"MT",99,99'

I cleared all the messages using "AT+CMGD=,2" and was once again able to receive SMS with the Verizon SIM in place. Since then, I received and read about 10 SMS messages and the list from "AT+CMGL=4" now shows 3 of them. There doesn't seem to be any connection between those 3 and the ones visible via "mmcli -m any --messaging-list-sms". These stored messages survive reboots and battery removals.

Problem 1: When I was trying to diagnose this problem I ran ModemManager in debug mode and it showed no hint of receiving anything from the carrier when a SMS should have been received - there were just occasional "Get Packet Statistics" and "Dormancy Status" messages that seem to be normal idle activity. Looking back at the 99-message-logjam, several of those messages were from that period. Apparently messages were received from the carrier, stashed somewhere, and then ignored - all without any outward indication.

Problem 2: If they made it this far why weren't they processed all the way through to the Chatty hand-off?

Problem 3. It appears that this clog is going to happen again as certain messages accumulate in the modem/SIM.