A maximized player window is displayed whenever the video is played, showing empty space to the left and right of the video.
No such problem for landscape orientation videos.
Screenshot of what I'm talking about:

See the black space to the left and right of the video?
I really hope this gets fixed, maybe force VLC to 'auto-fit' portrait videos to the last remembered window dimensions etc. Thanks!
Settings
Zoom: 1:1 Original
Aspect Ratio: Default
Crop: Default
Software
Windows 10 64-bit
VLC 3.0.4