Slideshow gallery wrong auto-sizing images

This is brand new issue to me – appeared on a 3 years old install (all updated):

When images are displayed in WP native slideshow gallery, some images overflow out of the gallery and overshadow the text below the gallery window.

Until recently the vertical images were re-sized to match the height of the gallery window and the difference in images proportions was compensated by gray area on both sides.

Now all images are re-sized to mach the width of the gallery, but the bottom of some images sticks out from the gallery and overlaps the text below.

It appears the issue is to some degree browser and operating system dependable. It shows only on some computers.

Any suggestions how to troubleshoot and fix this – please?