Can't open projects while Mercury Transmit is on
From a fresh startup of Premiere, opening any project results in an everlasting beachball of death while Mercury Transmit is on. "Easy" workaround is to do a clean launch of Premiere (don't open from a .prproj), disable MT, then open the project, then re-enable MT. It's very irritating, especially since I work on 2-5 different projects every day, and has been happening to me since PrPro 15.
MacOS Big Sur 11.4
Mac Pro (2019) 16-Core, Radeon Pro Vega II Duo, 128 GB RAM.
Two DELL U2719DCs (2.5k, USB-C), and a LGC9 65" (4k, HDMI).
Occasionally I'll use Blackmagic's DeckLink Mini Monitor 4k, for SDI+HDMI output, but I usually leave it disabled for Mercury Transmit.