Why Premiere 2019 playback is better than in Premiere 2020? Now it's too luggy

[m.b.3d]

Hallo, I'm asking help to community and especially to Adobe cause the editing in Premiere 2020 is too laggy. This is my system:

AMD Ryzen Threadripper 3960X 24-Core Processor 3.79 GHz
RAM 64,0 GB

Windows 10 Pro Version 20H2
Build 19042.685

Windows Feature Experience Pack 120.2212.551.0

GeForce GTX 1080 Ti (456.71 driver, cause the last NVIDIA driver make crashes with Premiere...).

The test I did is simple: new project (in the same drive path), the first one with Premiere 2019 (13.5) and the second one with Premiere 2020 (14.8). Importing a mp4 clip in a 1080 sequence, playback with no render. Result? Premiere 2019 works fine, Premiere 2020 plays with awful lags. So where is the problem? What's the fix suggestet from Adobe?