I’m working on 2019 iMac 8core/Vega 48/32gb ram/2tb ssd/16tb external tb raid/
OS is 10.14.6 and Premiere Pro 2020.
I was getting video playing back at 1/2 speed while audio was normal – right out of the box!
Drove me nuts. I never had this problem in 2018 PP
I have a 3 monitor system and 3rd monitor is out through the black magic ultra studio mini monitor.
My fix.
I went to premiere pro-preferences-playback and deselected all my video devices. Then select ok.
Then repeat the process and select the video devices you want. Then hit Ok.
This removes the video lag for me every time.
Hope this helps.
Best of luck!
CK