So you’ve updated to 22.214.171.124 and your featured images are gone and you think this is a bug. Actually, it isn’t. It’s in fact a fix of a previous bug (which, apparently, you were using to make Mantra behave in a particular way).
The bug consisted in the fact that full posts used to display both the featured image and any images inside the post – which is bad.
The new behaviour is to display featured images only in “excerpt” view, not full post view. So in case you are using the <!–more–> tag, you are actually viewing full posts, not excerpt, so your featured images will not be displayed.
To resolve this, you need to either switch to “excerpt view” (and set the desired excerpts to posts) or insert the desired (featured) image at the beginning of the posts (specifically before the “more” tag), so it gets displayed on the website.