After the last update(r267 steam, win 10 64bit), if you minimize and maximize the program, Constract 2 takes the from the left monitor, instead of the main one, this compresses the event tree...
It also happens to me but I had not made an error report.
https://www.construct.net/en/forum/construct-2/general-discussion-17/problem-with-c2-141297
I can't reproduce this in r272. I develop C2 on a dual-monitor display and have never seen this, so I would guess it's something to do with your specific system setup.
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In r272, this bug was gone. Now everything is all right.