I am almost certain this is a bug, I have been using the master effects section of the realtime vst effects, very helpful. But after downloading the latest version of Audacity (3.6.1) every time I have tried to export multiple tracks, all the tracks will render fine, but will just be silence. I know it is master effects because exporting with no effects results in exactly what I would expect from rendered audio, and using track by track realtime effects results in perfectly as expected audio as well.
I can also confirm it is not the used plugins. I tried with two different MuseFX plugins as well as Graillon 2, when any of them were turned on the rendered audio was silence.
This project in particular will not export usable audio unless the master effects are turned off. Though it is worth noting that I have been able to replicate this in any of my other projects with master effects with many different combinations of effects as well as single ones, I will try reinstalling Audacity to see if that helps, though.