Depends on whether on the compressor or turbine blade. I would go with the stick on in the lower temperature and clip on for the higher temperature blades.
Lead substitute for environmental considerations.
A balance issue cropping up with the engine or the fan itself would be almost impossible, unless one or the other threw a blade.
I’m thinking some sort of acoustic resonance. There’s a lot of very high energy airflows going on in and around around that fan. And there’s could be interesting stuff with that high-bypass engine. An acoustic resonance could drive mechanical vibration in turn.