See Blue Robotics Forum for the entire thread but here is the short version:
We saw odd wear on a T200 thruster prop and found that the grub screw was loose, allowing excessive lateral travel of the prop on its shaft. The telltale signs seem to be squealing or excessive lateral movement.
We learnt that it is a simple process to check for excessive travel or lack of travel and tighten grub screw by removing the rear cap where the power cables attach, locate collar and spin the prop to access the grub screw. The shaft seems well positioned with about 1mm extending beyond the collar.
Blue Robotics said that the setscrew in the shaft collar can loosen over time, and should be checked and re-tightened periodically. A bit of non-permanent threadlock can also help with this, as long as it is applied sparingly and does not interfere with removal of the setscrew for the recommended maintenance. Transportation by ground or plane can introduce vibrations which speed this loosening up. Removing the nosecone on the front of the thruster is the easiest way to access it.
We suggest regularly checking prop shaft lateral travel on your T200s.