I've just updated WP Offload Media (https://deliciousbrains.com/wp-offload-media/) to v2 and I now can't upload images to my site. Either the media library doesn't load or I get http errors when uploading. If I disable Smush Pro then it works fine again. Similarly if I disable WP Offload Media and have Smush Pro enabled it works fine. So it seems to be a specific conflict between those two plugins.
I've contacted the plugin developers of WP Offload Media too but wanted to let you know to see if there's anything that can be done.