Solved! Go to Solution.
Press and hold Side key until you see Power Off - select it to power off the phone.
Now, off to the Maintenance (Recovery) screen:
Press and HOLD the Volume Up key, and while holding, press and HOLD the Side key.
When the Samsung splash screen appears, release both keys. Within a few seconds, you'll see the Maintenance screen, with a number of menu options.
Use the Volume Down key to highlight Wipe Cache Partition. Press Side key, select "Yes".
Now, Use Volume key to highlight "Repair Apps" (should be last menu option). Use Side key to select it.
The phone will automagically restart. Let the phone settle down for a couple of minutes.
I just completed "Wipe Cache Partition and Repair Apps". A few minutes after completing this, my messaging app started blowing up again and resending old messages and etc. I have the Samsung S21. It is also happening to my mom and brothers Samsung phones. It is happening multiple times per day. Wiping cache partition and repair apps did not solve this problem.
I am having the same problem, as well as my mom and brother. It is happening more often and starting to get out of control. I just tried wiping cache partitions and repairing apps and that did not solve the problem. Please let us know if you figure out a solution!
I am very sorry to hear of the mass sending of messages, and can understand the frustration arising from this. If your phone or tablet is misbehaving, it's possible that a third-party app is causing the issue. To figure out what app is acting funny, you can use the Safe mode feature. In Safe mode, your device won't run any third-party apps. This allows you to easily identify and remove the app that may be causing the problem. Try this guide: https://www.samsung.com/us/support/answer/ANS00062983/
Please let me know if this helps.