I've had several users tell me they're not seeing personalized content on a webpage despite the fact that they have records, the properties being used for the personalization have content in them and I'm able to see their personalized content in the preview when I preview as them.
If they're using an ad blocker and/or not allowing cookies, I'm assuming that prevents the cookie(s) from ever being dropped and therefore there's no way to recognize them as that user - is that right?