Your phone has a feature that’s built in to Reset the phone once a Week so it might be worth just checking if that’s activated @ashley-x8
Settings > General Management > Reset > Auto Restart.
Ensure your Software and Apps are all updated.
If it isn’t the Reset feature then a rogue App may have caused it.
If this becomes regular then a good way of testing that theory is to put the phone in Safe Mode which disables all the downloaded Apps just leaving the Stock Apps active.
If it stops then it’s an App which you’d need to narrow down by deleting one at once until it stops.
Sideloaded Apps From Apk Files can cause issues.
If if after all this your phone still displays issues then try shutting the phone down and go through a set of button presses to enter into the phones file system and clear the phone system cache.
A last resort would be a Back-Up and Factory Reset.
After that a Samsung Service Location or Samsung Experience Store would need to run a diagnostic.
Hopefully it’s just a one-off glitch.
Current Phone ~
Samsung Note 20 Ultra 5G SM-N9860_256Gb SnapDragon 865+
Samsung One Ui 3.1/ Android 11.
The reason your phone resets itself is the same reason, likely, my phone resets itself. First, these phones were advertised originally to make things easier, speed up communications etc.
However, they failed. I've watched over the years as phone companies failed left and right to provide service, they blamed it on "user error" among other things, then they started saying "not enough coverage". BRILLIANT. Now though, we know, even to comment, I had to expose my phone, I had to "allow" access to my phones sensitive files. WHY? I've long since discovered I can use the old card catalogue and find a book faster than the computer. The answer to why your phone keeps resetting itself is, simply put, you gave away any rights to privacy when you activated your phone and signed away your rights, now, they have access to your "sensitive files". I wonder if anyone knows how easy it used to be to make a phone call? These things have seriously slowed down progress, and hinder development, not a "statement" just an acknowledgement, if you pay more, you might be protected from one invader, but the cost $$$ of all around protection is up in the neighborhood of "government costs" (millions). Other than that, you must know, you use these things at your own risk, they will NOT fix it, so, keep asking, you'll see, you'll continue to get the runaround, the blame, and the bill, enjoy the future.....