Yesterday I was testing some button remapping on my controller and saw that you could map "actions" as well, so I mapped the screenshot function to a button to test it.
I activated it, then mapped it back after seeing the notification that the screenshot had been taken, and entered a multiplayer game.
While I was playing, some time later I got a notification that looked like a demon had possessed my Xbox, telling me that the screenshot had been uploaded.
I was unable to take a photo of it because I was busy in multiplayer for quite some time and today the notification is back to normal, so the best way I can describe it is that I used an online "randomizer" to generate some text, and the notification that normally says "Screenshot uploaded to the Xbox network" looked something like this:
S̴͚̒c̴̘͚̑r̵̩͠͝ę̵̰́e̸̤͈͊ṋ̷̯͠s̶̛̱͘h̶͈̭́o̵̞̲͛t̴͔̫͗ ̸̦̑̚ṳ̵̩̿p̶̈́̚͜l̵͖̎ò̶̢̤͆à̷̢͚d̶͈̃̆ę̶͙̿d̷̫̫̿͐ ̸͕̔̀ţ̸̩̾͛o̷̙͔͊ ̴͈̿̉t̸̖͈̃h̸̤̒̈́ê̶͈̪ ̸̡̀̽X̸̠͋b̵̪̀̄o̵͚͚͝x̵̱̪͒ ̵͙̎n̷̠̓e̵̗̠̊t̸̺͙́͠ẘ̵̧̼ǫ̷̋͐r̵̼̯̽k̵͓̬̆̓
It wasn't as bad as the above example but it had lots of these weird accents on every character.
Today the message is back to normal. The Xbox has just been sleeping inbetween, no hard reset or full restart.
Does anyone know why this happened and what the reason was?
This is Xbox Series X.
OK; Scratch "nothing happened inbetween", I now see that there was a system update early this morning. While I don't know if this update fixed anything in this regard, I would assume the console did some kind of restart at the time and my game just continued from Quick Resume.