As you may know, the beta grid is usefull mainly to try uploading mesh assets without having to pay for the upload until you have the uplaod settings right and use them in the main grid.
You would have noticed that when you log off the beta grid and log back into the main grid your cache starts loading almost from zero and that means you better stay still and wait for it to load completely to avoid any inventory issues.
This happens because as time goes bye without you having changed your user password, most of your cache for the main grid won't be replicated into the beta grid cache, so after you log back to the main grid it's like having deleted from cache all new items you got in main grid since you logged into the beta grid for the first time.
A solution would be to reset your user password and log into the beta grid, which will also update your inventory there to reflect the inventory you currently have in the main grid. But if you don't want to change your password and don't need your inventory in the beta grid to be updated with your latest stuff you can make use of multiple viewer instances.
The trick to avoid caches to load from scratch after using the beta grid is to enable Allow Multiple Viewers option in Preferences / Advanced and then, log into the main grid before you log into the beta grid using another viewer instance. Being logged into the main grid while you log into the beta grid is the key technique that prevents caches from losing items when using both grids.