Just went thru a similar thing with my 2015 r-31. The feeding rubber tube that routes the stick from the top of generator to the oil pan had tore free next to were it goes into the engine block. The stick was going thru the tear and ending up outside the engine, it got wedged on the outside of engine and would not come out. I pulled so hard the yellow top portion of the dip stick broke off, next tried to pull with locking pliers with no luck. Took front cover off generator and found the problem. Called Onan and they covered it under warranty, sent me new dip stick and the feed tube. Looks like just a bad design. Good luck, it's tough getting that front cover off enough to see the area were the stick feeds into engine block. This is my first reply so I hope it works and helps?
Dayle