I've been flying the DJI Mavic Mini for more than a year now, and recently I've been getting warnings from the DJI fly app saying "propellers rotating too fast" forcing me to return and land. After landing, one of the propellers start beeping, and it's a different set of propellers every time. But whenever I check the propellers for damages, I never find anything unusual. The blades are normally shaped, there are no loose screws, and it spins perfectly without any issues. When I fly it again, everything seems to be normal. That's until about 10 minutes into the flight, when the same warning appears again, but on a different propeller. And I still could not find any damages after a detailed inspection. Can anyone help?

Hello there. I am sorry for the trouble this has caused and thank you for reaching out. may we please know before this issue happened was there a hard landing or a crash that happened to the your DJI Mavic Mini for us to be able to isolate the said issue? Thank you.

You cannot tell just by looking at them whether the propeller blades are sufficiently twisted to cause degraded lift.  But doing a hover test, and analyzing the flight log dat file to plot and compare the individual motor speeds will tell you for certain.

See this thread posted a year ago for a detailed explanation including photos and data plots.

Motor Speed or Propeller Speed Error - How to avoid.
forum.dji.com/forum.php?mod=viewthread&tid=227318

^ That. Eyeball is useless for this because the deformation only needs to be minute. Just replace props when a pair is flagged by the beeping ESC. If you really want to be sure you need to analyse the dat file from the flight, inspect rotation speed for all motors during hover test.