I experienced similar results a couple weekends ago. What I found when
I took a straightedge to my outfeed table is that it is not flat - it
curves up the further it gets from the knives. Sigh. I'm going to try
to take it to a machinist and see what he can do. I'm pretty sure the
jointer is out of warranty - it is a 1952 4" Craftsman.
-John