Dude your RAM chips are overheating (99% certain) - that's why it's specific to certain bandwidth heavy games.
The PS4/PS4-Pro fan blows out the back and is supposed to suck in through the slits on the side - the air entering on the side goes both under and over the main PCB - the RAM chips are on the underside of the PCB and covered with a metal plate that acts as a heat diffuser.
You can see it here
https://www.ifixit.com/Teardown/PlayStation+4+Pro+Teardown/72946
Image from ifixit of bottom of PCB - see the RAM chips - the metal plate has conductive pads stuck to the metal plate above (you might want to check/replace these too if you really want to be certain)
Don't take my word for it - eg
Sony Engineer Compares PS4 to Formula 1 Car; Shares Detailed Schematics and Info on Cooling Solution [comment the PS4-Pro cooling design is the same]
(
original japanese www.inside-games.jp)
Here's a diagram (it's upside down in the PS4/Pro) :
(grey: heatsink ; blue: fan ; red : APU and RAM ; dark green : PCB ; light red : PSU )
If you cut a hole in the top the fan will suck through there, and won't suck through the case, so your PCB won't get properly cooled. The RAM can get too hot even when the APU isn't working that hard if there's a lot of access ..
(ton of other people told you this too)
You need to cover/close that hole you cut.