I am also seeing issues when a group is snapped left or right. I have two identical monitors and these groups are on the rightmost monitor.
In the group to the left I have Outlook O365 and Teams O365, and in the group to the right I have Take Command (CMD replacement) and P4V (Perforce Visual Client).
What I am seeing is that the left group overlaps into the monitor to the left of it as well as over lapping the group to the right. Both programs in the group to the right seems to be properly snapped, but Outlook and Teams don't seem to know how to stay in their space.
I tried swapping the two groups. It looks like which ever group is on the left spills over into the monitor to the left. The Outlook/Teams group still doesn't stay in their space at all though.
When I first snap Outlook and Teams, they are correct but as I select them and others going back and forth doing work, they start overflowing their "snap" boundaries.
1) Windows 2004 (OS Build 19041.388)
2) 'You have Microsoft Teams Version 1.3.00.19565 (64-bit). It was last updated on 7/16/20.' and 'Version 2002 (Build 12527.20880 Click-to-Run)
3) 1.39 beta
4) 2 identical side by side, 2560 x 1440, landscape, 100% scaling
Since screen shots won't show overflowing onto the other monitor, I took actual photos so you can see the physical monitor.