My phone regularly changes the wallpaper even when locked. Today, it changed the clock from digital to analog, applied a "warm" filter to the wallpaper, added some random text and emoji to my "emergency contact" message on the home screen, and replaced the left shortcut from phone to some random app. When I took my phone out of my pocket I almost couldn't recognise it!
On the plus side, I finally figured how to change the emergency contact message (I realized two months ago one of the digits of my emergency contact number was wrong - and it had been wrong for at least two phones/6 years now!)... so it evens out.
ps: posted from a forgotten draft from 11th April 2024
pps: I now protect myself from in-pocket shenanigans by always keeping my phone screen side up!