I bought the biggest bundle a few years back and a month ago I bought all the remaining books. I noticed on my puchase a month ago that I can't access some books like Wildemount and a few others. Some worked and some didn't. Can someone help me with this?

Check Your Marketplace to make sure your Entitlements are in sync.

Also, by access to a book, do you mean being able to read the source, or being able to use the Character Builder options? Because to use much of Wildemount on a character, you need to enable Critical Role Content in the HOME | Preferences so that the toggle is red/to the right. Other books may require Magic The Gathering Content enabled or Non-Core D&D Content enabled.

I was trying to read the book. The content seems to work in Character builder but I can't read a lot of the books I purchased. I did check the sync and it said everything was in sync. I think i have access in the character builder but not able to read the book itself. 

Hmmm so when you try to read Explorer's Guide to Wildemount it doesn't let you get past the table of contents?

If you re-check the page where you checked your entitlements, scroll down to Current Product Licenses and make sure Wildemount and the other new books are listed there.

If they're not in the list, there's a chance you may have been logged into a different account when you purchased them (purchases via the App are also prone to this), in which case you'll need to submit a support ticket.

It shows them in my puchase history in my last order. This is the only account I have as well. I puchased it via browser as well.