I have Note 20 Ultra 5G with AT&T and this issue started happening sometime last year after I replaced my other Note 20 Ultra 5G under warranty.
Every time I restart my phone I get bombarded with old messages as "unread messages" but the issue is that they have been read already. They don't really come in as brand new messages to the top of the list. They stay in same position as they were, still back dated to when they first were received and read. This can be anywhere from a couple of messages to bunch of messages. There is no rhyme or reason for the age of those messages that get re-notified.
Please help because this is very annoying and since this has been happening for a long time now and it seems that some people have had this issue for even long, it is ridiculous that Samsung or AT&T still do not have a solution or at least give a reason why this is happening!!!
Solved! Go to Solution.
Tap and hold on messages app icon and then in the pop-up tap on the "i" mark. Then tap force stop button and then scroll down to storage and clear cache. Do your testing to see if it helped.
If didn't help, do the same as above but this time tap on clear data and test again. Clearing data might reset some of the settings in your messages app.
Thank you for reaching out. I understand your frustration with duplicate text messages after restart. Please review this link with similar concern. Please view this link: https://us.community.samsung.com/t5/Galaxy-S-Phones/Duplicate-text-messages/m-p/84409#M8699