Stops mousetracking after i move mouse in specific place on second monitor

[eyehol3]

macOS 10.15.7

I have two displays. Upper blue square is external monitor.
The problem is, if I put cursor on the upper monitor, THEN if I move mouse over red lines, from up to down - mousetracking completely stopos, only quitting and starting over helps

Maybe it's cause of dpi? my monitors are:
top: Built-in Display 15,4-inch (2880 x 1800)
bottom: DELL 2007WFP Display 20-inch (1680 x 1050)