I am a Master Tier subscriber, my entitlement data is in sync, I logged out and logged back in and I still do not have access to the 2024 PHB on both the web app and mobile app.

I've seen some say that I would need to pre-order the book as well as having the subscription. I hope that is not the case.

Yes, it requires Master Tier subscription as well as a pre-order of the 2024 PHB.

So to have early access, you also need to order the book? Or even when the books comeare people still going to need to pay 30+ Dollars for 90% of the game?

Yes. You need to buy the book. Master tier just gives you content sharing, Maps, and a few other things.

They have put a large subset of the rules up for free, but it's not yet all the classes, and it's never gonna be more than one subclass each.

Did you purchase through the app? I heard someone say during Vecna: Eve of Ruin preorder days that app purchases take up to a week to process. I can't verify that myself since I only buy from off the website.

If that is not the cause, the only thing I can recommend besides reaching out to Customer Support is clearing the cache. I saw that work for some PHB preorder people.

This is all assuming that you bought the book at all. The OP can be read to mean that you are hoping the sub granted access alone. The sub only grants early access if you have it and also bought the book.