Similar issue to https://wordpress.stackexchange.com/questions/2850/404-when-fetching-image-from-wp-content-uploads, though their fix did not help my issue.
After updating WP, many images are suddenly missing from the site. I used Inspect Element and saw they're 404'ing, though they definitely are in the media library. Oddly, the media library thumbnails for the 'missing' images are also gone- but clicking on the blank thumbnail shows the full image to be there.
I tried several online solutions, including disabling all plugins, removing the .htaccess file, optimizing images, and deleting the cache. No luck. I haven't tried manually reuploading because there are 3k+ images on the site and I want that as a last resort.
I can send the site link privately on request (it's a company site).
Many thanks.