I would lay the windshield flat, activate wipers, and watch and see if you can see anything specifically catching. Hard to say anything without any eyes on it.
If it is an aftermarket frame, the problem is that the mounting points for the pivots and motor aren't located properly. It isn't that there is anything for the wipers to hit/catch on, more a case of binding.
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This will fit all YJ Wranglers 1987-1995. Just what is pictured, with the nuts. Wrangler complete front wiper motor, transmission and linkage in perfect working order. Tested thoroughly. Includes plastic nuts.