As has been said by others, there may be more than one cause of secondary pois.
One subgroup of cases with secondary pois have had surgery or trauma (ex/ vasectomy surgery or varicocele surgery).
I find the case described below very interesting because it is complete: pois was diagnosed, a physical cause was identified, treatment (surgery) was provided and the patient was cured.
The whole article is worth reading, as well as describing one particular case, it is an excellent overview of pois.
https://pmc.ncbi.nlm.nih.gov/articles/PMC9226701/"In our case, we hypothesize that POIS is caused by repeated contact of the sperm or epididymal fluid and circulating T-lymphocytes in the seminal tract. Moreover, epididymitis may increase local vascular permeability, which may increase the possibility of blood and semen exposure. Therefore, we believe that epididymectomy and vasoligation are effective ways to eliminate the influence of these two factors. "
Another subgroup of cases (possibly primary and secondary) have low T / hypogonadism so a completely different cause.
Here's a case which is again complete: pois diagnosis, cause identified, treatment and cure.
https://www.sciencedirect.com/science/article/pii/S221444201930453X"...the possibility that testosterone deficiency may be an underlying etiology in some cases"
More on the blood testis barrier - bit more speculative:-
https://poiscenter.com/forums/index.php?topic=4364.msg47224#msg47224https://poiscenter.com/forums/index.php?topic=4353.msg49432#msg49432As for myself, I have primary pois since puberty so it's more difficult to identify a cause and that would belong to a different thread. But I'm searching for common ground and I hypothesize that perhaps issues with the blood testis barrier, regardless of the cause, could be a similar issue of some primary and secondary cases.