No notifications when I text myself

I have the same issue. Schedule texts (with the regular Samsung messaging app) on my S21 Ultra to myself stopped either on Jan 18 or Jan 19 2023.  As the last text that I got a reply on was Jan 17, 2023.
I would use this all the time to send reminders to myself and miss this so much. 

When I realized that I had missed the first reminder I call T-mobile support in February.  They got up to a 2nd level tech since the 1st level tech didn't understand the issue.  The 2nd level tech even acknowledged that you should be able to do this.  He said he would have customers send themselves a text to verify that a phone was working. Unfortunately he was not able to do any further troubleshooting because at the time they were having a system issue.  He told me he would call me back in a few days but I never heard from him again.

I've tested this on my the other android T-Mobile phones in our house and we all have the same issue. They are all Samsung's so I'm not sure if it's a Samsung software issue but if I recall correctly the tech had an iphone and it was happening to him too.  I hope that they can fix this so I can start sending scheduled messages to myself again and get the replies.