A couple of thoughts -
1. Use a sharp box knife and cut that leading protrusion off of the PVC fitting. This should allow a better capture of the threads.
2. Switch to using a PEX connector.
Had a similar thing occur on a friends trailer RV last week - that trailer had a quick release outdoor shower attachment that the hose connection from inside the coach was poorly assembled. I happened to have a 1/2” PEX faucet coupler in my box but the rubber seal washer wouldn’t allow it to thread either.
But as opposed to what you have pictured, the male side wall fitting didn’t have a beveled ID to allow the washer to fit into and seal against. I used a sharp box knife to cut the smoothest bevel inside of t fitting.
It took some umpf, but I got the threads started and the assembly tightened together with several turns of threads.
‘91 Ultrastar Champion‘02 Georgie Boy Landau 8.1l Workhorse
‘03 Jeep Wrangler TJ 2018 Jeep Wrangler JK toad