Wrong Aspect Ratio

When I play movies, some display just fine, and some are stretched vertically (within the same add-on). I’m supposed to see black lines on top and bottom, but instead of that, the image is stretched vertically to fill the whole screen. The movies that are displayed correctly also take up the whole screen, but are not stretched. I mostly watch recent movies, so I imagine they all would have the same aspect ratio, no?

I have the Kodi option “Minimise black bars” under video settings turned off. The TV setting to Auto (and I tried all the options).

Does anybody have any suggestions?

Thanks in advance!