When we try to Browse to select an image for an image field, nothing appears in the Select Media dialog though we've confirmed there's content in the folder designated in the field's Source attribute.
(This happens for both the tree view and the list view.) If we then go through the Upload Media procedure, the upload completes (as verified by examining the designated folder) but the Select Media dialog remains empty, as does the affected image field after closing it.
Pertinent details: we are just completing an upgrade from Sitecore 8 to Sitecore 9.2. (I think it was behaving something like this in Sitecore 8, but can no longer confirm it.) We're using Lucene search, not Solr, at this time and have made a point of rebuilding the
sitecore_master_index (along with a couple of others), knowing this can be a factor. It may also be worth noting that, in the pre-deployment environment I'm currently working on, the designated folder for this upload is very big - some few hundred files - and takes several minutes to load browsing the Media Library, yet the "No items found" message in the dialog comes up within a few seconds.
Any insights or advice are welcome.