In the past few weeks I experience problems attaching screenshots in answers.
Steps to reproduce:
1. I enter some explanatory text in the answer.
2. Then I use the button Insert Image (the image is usually located on my desktop, but I also tried attaching images from D and C drives).
3. After clicking the Upload button I can see the progress indicator flashing for a second, but there is no popup to confirm the image upload.
In the console I see the following:
I also noticed that the vertical scroll disappears (I cannot scroll up to see the question text unless I refresh the page).
I can attach the same image to questions and comments without any problems.
It seems that the issue is not related to a specific browser - this happens in Firefox 64-bit (both developer and standard edition) and Google Chrome (the latest official build and the latest portable edition). It occurs in Windows 7 64-bit and Windows 10 and when I use different ISPs (no VPN).
I already tried deactivating add-ons, turning off Firefox protection settings, a portable browser with default settings with no success.
I have cleared the cookies and cache as well between attempts and I also tried accepting whatever cookies the site asked me to accept (even the advertising ones).
Sometimes I am able to attach an image after posting an answer and entering Edit mode.
Is there any other setting that I should check?