I do agree with you, for all we know, this could just be a hidden shadow ban, where ratings are voided because Roblox thought we are bots/abusing the system.
I found out that I am unable to rate ANY item, including “gamepasses, experiences, models, (ECT)”, so the issue is most likely built in a function that validates your ability to rate website content.
TLDR: Possible that requests return ‘false’ in the “rating validation” function. (therefor blocking us)