The page [[ https://en.m.wikipedia.org/wiki/Wikipedia:Extended_image_syntax#Vertical_alignment | WP:EIS#Vertical_alignment ]] has some examples of the vertical-align parameter for images. They don't appear to work on Minerva; the image tag has class="image-lazy-loaded" and no vertical-align in the style parameter. Copying and pasting that section's code into the [[ https://en.m.wikipedia.org/w/index.php?title=Wikipedia:Sandbox&oldid=865647270 | sandbox (old revision) ]] works however; the images have no lazy-loading class and style="vertical-align: text-top" (or whatever was requested).
I don't have a reliable way to force lazy-loading of images on and off and so guarantee that it is the cause of the problem but it seems to be the cause; I did some further similar tests and the pattern persisted.
(Edit: references to MinervaNeue removed as the same bug can be achieved with the Monobook or Vector skin when using URLs like [[https://en.m.wikipedia.org/wiki/Wikipedia:Extended_image_syntax?useskin=monobook]].)