500iu hCG twice a week does not seem too high.
250iu EOD is 875iu/week.
The testes have aromatase, almost all tissue does to some degree. The big factor is that ITT [intratesticular testosterone] levels can be 80 time higher than serum. That is a lot of T for the aromatase to act on. Perhaps your testes are reacting to a higher degree to the hCG than usual.
When you take aromatase, the concentration in the tissues of the testes will not be higher than found in other parts of the body. Thus with high ITT levels, adex is not very effective in the tests as the ITT overwhelms the adex. Adex is a competitive drug.
For guys who have testes that strongly produce T when on hCG, the dose of adex required needs to reduce E production in general tissues by a further amount equal to the E production in the testes.
To achieve a certain serum level of E2, there will be some tissues that may have E2 levels that are too low. Some tissues create E for local needs and the increased adex load might be adverse in some tissues. This is all just my mind wandering and there may not be anything of this sort that has any consequence. Many things will never be known.
You really need new E2 lab work! You can always take an adex bump dose and try to read what is going on by how your mood and libido are react. The mood downside can be quite significant for some if E2 goes too low, probably in part from reduction if T-->E in the brain.
If your testes are larger/recovered and firm, you can try a smaller dose. If the hCG is the cause, injecting 250iu at a time EOD might be helpful. Certainly a low cost experiment.
For older guys who's testes have limited hCG/LH response due to tissue aging or damage, hCH use will then generate less E. This means that results will vary.