Cubabse 12 on OSX 10.14.6 VST instrument tracks stopped working in project

Hi, wonder if you can help. So was working on a project with a few VST instrument tracks (omnisphere) and all was fine. Bounced them down, did some processing of the audio in another project. Went back to the project to make some edits and for some reason the VST tracks are now not working at all: they do not sound and even the keyboard is not responding via MIDI. So frustrating and tiring to troubleshoot. It was working fine and now the keyboard is not responsive. No idea what caused since i just re-opened the project. Can someone pls help? this isn’t going to be a regular thing is it?