Same issue as noted in other posts. Motor speed error. After landing and motors were shutdown, left rear motor ESC was beeping. As I had only flown about three minutes, I powered off the drone, then powered it back up and flew the rest of the battery. Mini flew fine and no more error messages.
View attachment 99583 I did not replace the propeller as suggested in the dialogue box.
I’ve attached a picture of my flight time when the error showed up. I had been hovering for about a minute when the message appeared. I then returned and landed.