How to get rid of grey block under poster images?

Site URL: https://www.stoneboundpigments.com/

I'm having trouble with some poster images on my home page, they appear with a light grey rectangle below the images. When I got into edit mode they disappear so I can't tell what it is. I've tried re-sizing the images and swapping them around but can't figure it out... Any ideas?

I change the text overlay with CSS a while ago to have the text appear at the top and with a transparent background, but that was months ago and this only started yesterday.

Thanks in advance! Here's some pictures of what's going on:

Having the same issue on our site: https://www.deseagrant.org/coast-day-2021-i, with the overlay below the poster block images. As with your experience, they look completely normal in the editing environment.

Strange thing is, they looked fine for a while, and then completely changed without any sort of editing/interference, as if they just stopped working overnight.

It looks fine here. Did you solve this?