I'm running a multisite install. On the main site I uploaded a couple of images fine this morning. I then updated some plugins (which I have since turned off for troubleshooting).
Some images are refusing to upload. Sometimes one of those images claims to have an upload error but it appears in the media. It cannot be viewed or edited, and there are no options for inserting a different size image (s/m/l). These images were sent via email from a client (in case the metadata has anything to do with it). The php upload limit is 8mb; these images are 3-3.5mb.
Other images upload fine - ones that did not come via email and were already on my hard drive. There are s/m/l size options for inserting them into a post or content. Most of the time they cannot be edited - no cropping or rotating. Every so often I'll be able to crop or rotate an image but I can't related it to anything specific (like turning off plugin X or clearing the browser cache).
I'm stumped, and it seems that similar problems exist for other users of 3.9 or 3.9.1. How can I resolve this without resorting to restoring a backup from 24h ago?