Images Suddenly Missing

I've been using Clean Journal for my non-profit site without any issues for several months. Been thinking about asking our Treasurer to consider upgrading us to Pro. But now, 2 days ago (June 5, 2016), the bulk of our images have inexplicably vanished, and the Featured Slider is only recognizing 1 image (sporadically and only on desktop browsers). The site logo at the top left is the only image that is loading, and that's only after I deleted it and reuploaded it to the Media Library, but for pretty much everything else, that didn't work. None of the settings with/in the theme customization were changed. All the images are in place and linked correctly as featured images. The featured slider is still enabled, etc. I made no changes to the theme at all before this happened. I double-checked everything afterwards and couldn't find any reasons for this issue. I *did* update 2 plugins (Akismet & TinyMCE) recently. But I've already tried deactivating both of them to see if either of their updates caused the issue, and the problem continues with them inactive. I have seen several people on various sites stating issues with the newest version of WP having missing images with various themes, so am tentatively wondering if that could be part of the problem? That the newest WP is incompatible with the Clean Journal theme for some reason? Overall, the theme is working - all my menus are in place, all the pages load . . but only 1 of the 4 featured images load for the slider, and many pages are displaying text in place of the images now. All of the 4 featured pages *do* have their correct featured image set. Without the slider, the first page of our website isn't nearly as appealing/eye catching. Several images showed as broken in the Media Library, so I removed and reuploaded, and then redid all the featured images on the pages they went with, and still nothing. Would love to figure this out. Clean Journal is by far the best theme I've used for our site so far, and would like to keep using it, if I can get our images back again! I'm seeing these problems in FireFox and Chrome, both of which are up-to-date. That is on a desktop PC running Windows 7. On my iPad mini, which is also up-to-date, no images, including the lone 1 mentioned above in the featured slider, are loading at all. That is with Chrome & Safari. Have also tried cleared cache, cookies, and offline website data. Do not have a caching plugin on the site. Site: http://www.southwestdi.org Any ideas? Thank you!