Aloha s. Bummer and a real PITA,
Occasionally I too have this happen to one project and I could
never find the cause.
Here is one approach:
I would render (export) all MIDI and audio files and then import them
back into a working project.
Take screen shots or cell phone pics
of all eq’s FX’s values etc and then
enter them into the new work.
Upside:
this will work,
(unless you get crashes during export)
Downside:
Time consuming. Very time consuming.
HTH (hope this helps) and Good Luck!
{‘-’}