Doesn't matter if your window is open full size or closed into tray, when you open with the tray icon or a notification it gets shrunk, ignoring the last placement. Opening any other way works like it should. If needed, when Unigram's windows is closed and you open it like that, it opens properly at first, shows the logo, and then makes itself smaller.

It's been bothering me for months and there have been numerous Windows updates so I don't think that's the culprit.