CUBASE 11 PRO audio playback sudden change

Hi guys,
After using Cubase 11 pro since release with no problems on Mac (Mojave),
all of a sudden it seems to have wigged out and about half of the audio tracks in a project don’t send sound to the output while clearly playing in the meters, while the others do.
For example: A 100+ track orchestral mix with all audio showing in meters only passes Percussion, Harp, Piano etc. while Brass, Woods, and String groups are inaudible even though meters are showing audio and nothing is muted (There is a faint bit of woodwind coming from reverb send though but nearly inaudible).
I opened another project in CP11 and it did similar, so I opened another project in CP9.5 and it worked fine with all tracks playing as showing in meters etc.
So it seems as if something in CP11 has tripped on something for playback???
I did open the studio tab to check all was ok with my project after loading, and pressed “cancel” at bottom of tab so as not to change anything, is all I can think of that could have caused it…
So I’m thinking maybe a re-download could be a solution??? Any ideas?
Thanks for reading and any help!
(Mac Pro 2013 OS Mojave, Cubase Pro 9.5 and 11, RME UCX)