If the cpu usage is higher while no audio than with audible audio, it most likely is a problem with denormal (veeeery small) floating point numbers. Those will cause the CPU to enter an “high precision” / extremely slow special processing mode, which totally messes up performance.
Maybe a workaround is to enable auto suspend then, but denormals can be considered as a bug and should be reported to the plugin vendor. So it might be good, if you really determine here which plugin is causing the problem, since it also can be any kind of fx processing plugin, too.
It even is possible that Vital is not the cause, although it seems so. Maybe Vital is just not outputting really a zero value on idle, so then it triggers some processing vst, which then could have a problem with denormals. An accurate test would be here to remove all fx, save the project under different name, reload it and check, if the problem still exists, etc.
If the cause is a processing fx, then a workaround might be to add a dithering plugin before the fx, so the noise floor never drops to denormal levels (which are insanely small, nobody needs any processing in that area).