When I open Chrome window in other activity, all Chrome slows down a lot

When I open Chrome window (by clicking chrome icon on a launch bar or sending existing windows to other activity) in other activity, all Chrome windows slows down a lot. it has ‘stutters’ / ‘freezes’ for 1 second, every few seconds.
When I move that window back to first/main activity, everything works normal again.

I’m using newest Kubuntu.
plasma: 5.27.8
frameworks: 5.110.0
Qt: 5.15.10
kernel: 6.5.0-14-generic (64-bit)