2.0TDI 184hv coolant issue

So I have problem with my 2015 octavia 2.0tdi 184hv.

I can drive the car normally for how long ever I want, but when I floor it a couple of times, the coolant reservior is empty.

Some of the coolant is outside the reservior, but most of it comes back to reservior when I open the cap.

Already done: changed reservior cap, changed main waterpump, changed thermostat, checked for combustion gasses in reservior with combustion test, not the liquid one and there was no combustion gasses in reservior.

I think it should not be the headgasket, because in normal drive there is no problems.

Could egr cooler only give pressure to the system when I floor the car or could it be some waterpump, glogged radiator or leaking intercooler.

I did pressure test while it was cool and there was no leakage.

Also put 1 bar pressure to turbo and pressuretester on reservior and the pressure on reservior didn't go up.

Should I just buy the egr cooler or is there some test I should do first