Hi again,
i have with the same problem when I try to save or add a new product, I change debug mode to true and I only receive Error 500, but Validator it is ok and I do not display the error.
I have compared with another domain with the same version and I see this:
domain fail:
only launch 1 hook - moduleRoutes
domain good:
launch 4 hooks - moduleRoutes, actionClearCache, actionProductSave, actionProductUpdate