Try opening a new project with the original project open. Create a new sequence in the new project, then go to the sequence in the original project, select everything on the timeline and copy and paste into the new sequence in the new project. Hope that works for you, that was my only workaround!
No worries! I'm glad I could relieve someone else's pain! FYI, I haven't had this issue since in other projects. I couldn't tell you why though. It could be to do with updates, or it could have been to do with something specific within the problem project. Hope you never experience it again!
I think I've found the real reason for the bug. It's in video/audio codecs. When I try to export my projects in MPEG2 while using resampling - it exports with no sound. When I leave all export audio options by default - oh, miracle, here comes my sound back. I hope my efforts of wasting my half a night would help someone