I'm experiencing from the past few days these problems:
The Media File library is full of blank thumbs, sometimes three or four thumbs are fine, next minute you visit the Library again and those are blank too and another is right. Clicking on an image in the Library opens the Attachment Details box but there's no image, but if you click Edit Image the image shows up. When uploading I can't see any of the uploaded images.
Same in Album pages: When uploading images to an Album I can't see any of the images uploaded, neither in the Uploading dialog nor the Album page, here the images appear with a broken icon.
In the Appearance > Customize>Header Settings>Logo menu I can't see the uploaded logos. When visiting the website everything works fine (all images are shown) but logo. Sometimes it is there and sometimes it is not. When Logo doesn't show on the website, I can't see it on the live customization neither.
Last month I had a problem with social icons not showing that ended being a problem with AdBlock in Firefox, since then the plugin is deactivated on the site. I've deactivated the Firefox Content Blocker but problems are still there. I get the same problem in Chrome. Both browsers give me a "Mixed Content: some parts of this page are insecure" warning.
The permissions of the upload folder in my server are OK (755), I've installed a plugin to force thumbs regeneration, I deactivated all plugins but nothing has worked.
I attach some screenshots in a zip of the problem.
Thank you for your time!