Classical case of pinched belt/NO name belt/MALOSSI kevlar-belt or forgotten shim/ wrongsided washer close to crankshaft, between face drive and boss.
AND, this 300/500 belt is prone to hit the upper and lower metal part of your (any) CVT housing. Watched it without CVT cover. Thought something wrong with that, but NO, also with a NEW original belt touches up and down.
Might also cause more vibrations/ tear and wear on belt and faces. Even I could not see this on my own 500, where its CVT wasn't opened until I got it with 17000 km. One can see this black mark down there.
CVT of Xciting 300/500 has 3(three) different shaped washers to keep pieces exactely in place to avoid such accidents.
Also its oilseal at CVTs inner side has an important role in this mechanic.
TALKING ABOUT 500 CVT, others might not have.
IF everything is correctely assambled and torqued to exact figures, no Loctite is required.