I put a disc brake linkage kit on my FMS Pro Stumpjumper. It worked fine for awhile. Then I noticed how much the torque was bending the rotor and the linkage was bending as well. The bike shop cautioned me that it would compromise the braking because the bike wasn’t set up for it to begin with. After a season of riding wear on the axle seal was showing. I have since went back to the high quality V-brakes and will get use to the grinding sound when going through creeks and mud. These kits might work well for some bikes, but not the Stumpjumper Pro. Next bike I get will come with front/rear hydraulic brakes meant for it!

Who’s kit? who fitted it? brakes? hub? etc.

Specialized sold a proper adaptor for most of their FSR models, so either your talking about one of those aftermarket adaptors (fine if they fit properly) or whoever fitted it did a poor job.