I recently updated both CbB (2018, 08 Build 30)and Omnisphere to 2.5. Have been experiencing issue with the Omnisphere window being completely locked out. Some function do work on the main Omnisphere window but browsing patches on the left is locked. So i'm wondering is this a CbB issue or Omnisphere issue. The new standalone Omnisphere isnt affected...

Not definitive, but 2.5 is working fine here.

2.5 working fine here. Omnisphere sometimes causes a drop out when i open a project, but i currently only have 8 gigs ram so thats not helping.

I have Omnisphere2.5 it works fine for me.  Try it in standalone mode.  If not!  unfortunately you might need to uninstall it and re-install it.  See if you can change your omnisphere directory to HW that is where most of the new stuff is found.