Comment 3 for bug 1926216

I have the same issue and can add the following info which is hopefully useful.

My setup is 3 1920x1080 monitors.

When I try a mouse click&move operation on the left most monitor then everything behaves correctly.

When I try the same on the middle monitor the selected horizontal region is larger (as shown in the video). It appears to be extended (right of the cursor) by the width of the monitor (i.e. 1920 pixels).

When I try the same on the right most monitor the selected horizontal region extends off the screen (and I can't tell how far) but also the vertical selection is extended down by what appears to be the height of the monitor / 2 (i.e. 540).