After a bunch of testing (on Windows 10), this
seems to only happen when the upper-left corner of the OBS Studio window gets within about 10 pixels* of the left-edge of the left-most monitor (and probably any monitor that does not have another monitor to its left). This is because the check for if the window had a valid position only checked if the upper-left corner of the window was within any monitors. Jim has fixed this behavior in
this commit.
What's funny is that this definitely also happened in 0.15.4 (possibly also a bit earlier), but it only seems to have been reported now.
* The reason I say "within about 10 pixels" is that I noticed that the reported position of the upper-left corner of the window was sometimes off a little bit from the
visible corner of the window. My guess is that it has something to how Windows draws/composites application window borders. This seems somewhat consistent with what
@LuckyLIVE observed.