I loaded up Mixcraft and put the VST2 on one track and VST3 on the other track.
VST2 works fine, PCs received as expected.
VST3 WILL NOT receive PCs, as expected.

Are you SURE that you're using the VST2 version? Check your Plugin Paths in Mixcraft and make sure that the VST2 file is here:
C:/Program Files/VSTPlugins

And the VST3 file is here:
C:/Program Files/Common Files/VST3

This is the ONLY logical explanation for the behavior that you are experiencing.
Attached are 3 screenshots:

Mixcraft VST2 shows that the VST2 version accepts the PC#.

Mixcraft VST3 A shows that the VST3 version accepts a CC# OR a NOTE, proving MIDI connection.
Both CC# and NOTE will work to change presets. Most unusual implementation.

Mixcraft VST3 B shows that the VST3 version will NOT accept PC#, remaining in "Listening" mode as you described.