As Norm said the wear on the end of the joiner link looks like it was rubbing ,you could try putting the link around the other way so the clip is on the other side also the clip must be installed for the correct Direction Of Rotation. (your joiner link needs replacing)
I would also check the sprockets aren't warped ,bent or damaged and are not out of round with high spots also check the teeth aren't twisted ,bent or damaged .
Check any chain guides aren't excessively worn and the chain is not twisted and check the bearings aren't excessively worn and there is not excessive backlash on the sprocket shafts.
