as per title - have 3 campaigns (have deleted a spare as someone posted about a 3-max? ) that im doing atm. 

All 3 have content shared.

I have the Beyond Master Monthly sub atm

first one has all the books showing up ok. others only have a very limited selection ,  ive tried enabling/disabling/reneabling , tried starting a new campaign, and tried creating a character in the campaign and claiming it on case it needed to sync from that. 
I really need this sorted as its stopping me being able to run stuff..

any ideas ? :(

Do you own all (any) of the books on the site? The master sub doesn't give you access to any of the books. It only allows you to enable content sharing, which is everyone in the campaign will have access to any books that any player in the campaign has. This may be why you have different books showing in the different campaigns.

Also, the amount of campaigns you can enable content sharing with is 5.

yes i do own the books. Its shared them for one game, not the other 2, which is whats so odd :(

this should give you an idea of the discrepency  

ones it sharing : 

Player's Handbook

Tasha’s Cauldron of Everything

The Vecna Dossier

Try turning content sharing off and back on again.