Some time ago in the forum, people tested the hypothesis "allergic to their own sperm" by spreading sperm on their forearm, the place where doctors do allergy tests. [Careful: don't attempt a skin prank test at home, it can be dangerous, Dr. Waldinger warned. I mean just spreading sperm on top of skin]. I also tried this recently, to see if I'll get a rush or anything. I got nothing. I'll try again a few more times, just to be sure. The real reason, in my understanding, that the autoimmune theory was discarded was that also healthy men, with no POIS, also got reactions to this test.
Now, here is what I was thinking some time ago. We can try this but only with precum rather than cum. Just spread some precum on your forearm and wait for some time (like 24 hours without washing) to see if you get a reaction. I will try this soon, it's just that nowadays I have appointments with people almost every day and need to take showers - the moment I have some more time alone, I will try this. This would be a test for "autoimmune reaction to own precum." And then imagine if a control group of healthy men have no reaction - that would mean something along the lines of an autoimmune theory regarding own precum, rather than own sperm. It's an idea.
Look, I like the way you're thinking, we have to figure it out, who knows where the solution will come from. We have to think about all sorts of possible explanations and test them, as much as possible.