My webhost updated its MySQL servers' OS to Ubuntu Bionic and two of my sites both started having the same issue.
The sites have exhibits that are hidden from the index and appear as thumbnails on the section page. The thumbnails for these exhibits no longer show up. Text on the section page shows up properly.
URL is michaelmeyerphoto.com.
If I unhide the exhibits from the Index they appear as expected in the left nav menu. (Or top menu, as on spectaclebox.net, which I tweaked for the moment since I need this to be accessible.)
Any ideas? Thanks in advance!