The issue is somewhat moot.
Oneboxing Amazon links is against the T&Cs of their affiliate agreement apparently. My account was closed once because of it. Apparently use of their logo in a way they don’t sanction is misuse of their trademark?
They are probably actively blocking some user agents from crawling.
The best solution is to use their affiliate snippets. Agree this is a bit of a manual pfaff.
Maybe someone could fund or write a plugin to insert these snippets if they could be retrieved by api?
If you are not an affiliate consider using my onebox assistant to improve the tag retrieve reliability.