The bug is already confirmed by Adobe support (Bug Reference ID: DVAPR-4225210)
Affecting all versions of Premiere Pro v2020 and v2021 (+14.0 - v15.0)
The fix has not been sheduled by Adobe.
We're planning updating from premiere pro v2019 to v2020.
We tried it on some test stations and we're experiencing serious lagging when we start playback on a timeline or source monitor. If we press play it takes +- 1 second before the timeline starts playing. It doesn't matter if it's a long or a short timeline.
In Premiere 2019 we don't experience this behaviour.
What we tested already.
- It's happening if we use mercury transmit and send the output to an external monitor (Blackmagic mini monitor, ultrastudio, a Blackmagic pci card and Aja t-tap were rested and they all have that problem.
- we tested on a Mac Pro, Imac (pro), Macbook Pro (Mojave and Catalina) and an HP (Windows 10)
- If we disable mercury transmit ( not sending anything to a broadcast monitor )
the problem miraculously goes away.
- If we use 'Mercury playback Engine GPU Accelerate the problem is there, if we use Software only then there also is no problem. But than you can't use the benefits of the GPU.