I've only had a chance to test this with Notion as host so far, but I find that only newly instantiated instances of VI Pro get MIRx reverb. If I open an existing project created with previous versions of VI Pro and change it to use MIRx, it looks fine on the screen, but there's no reverb.
Dorico, Notion, Sibelius, StudioOne, Cubase, Staffpad VE Pro, Synchon, VI, Kontakt Win11 x64, 64GB RAM, Focusrite Scarlett 18i20, August Forster 190