Amazon S3 Media Source not allowing files to be selected

I have an Amazon S3 media source (Revo 2.6) all hooked up to a bucket, it works pretty good for the most part, you can upload/list files etc BUT it will not show any files in the resource browser, it does show all the files in the tree to the left of the browser, but none available to select in the right hand window. it just says "No files match the specified filter."

UNLESS

I remove all the items from the imageExtensions property. Took me a good hour++ of messing around with this stupid thing but now it does not show thumbnails.
Not a huge problem, though it would be nice.... the media browser WILL show thumbs for local files just not Amazon.

What is up with this thing?

Did you have spaces in the list of extensions in imageExtensions? If so, you may have run into this bug: https://github.com/modxcms/revolution/issues/13702

I had not come across that bug report, but had tried the image list (including .pdf) with/without dots, no spaces etc. it only began to work when I completely removed the list. Seemed to have something to do with the thumbnail generation lines 518 & 521 of mods3mediasource.class.php if I remember correctly. something about a divide by zero error?

Anyway - this only happened with the S3 media sources, the others were fine.