No smooth playback from timeline in Resolve 17.2.1.

Hi,
my footage is RAW UHD 3840x2160 50fps, compression 8:1 from BMPCC4k camera.
Footage is stored on SSD, see below.
RAW Speedtest shows very good results.

However, there is no smoth playback from the timeline in Resolve 17.2.1.

CPU load is 8% to 14%
GPU load is below 50%

I don't want to generate optimized media.

Who can help?
Thanks

I've found a weird one for me that works sometimes is just shoving over an adjustment layer on top of everything and it plays back smoothly, no idea why this works