I suddenly found that the Gravatar in my GitHub user profile had disappeared.
I then went to GitHub to upload the icon.
I googled the red error message, and read the last reply in this thread. Then, I had taken the above screenshot and started a new post on this issue.
Before I finished this post, the Gravatar was back again.
As not being a student/worker in IT, I shouldn’t spend much time on developing tools and finding a good solution to a strange problem. Instead, I should use others’ tools to save time and tolerate some faults, as long as I get the job done. Developers will work on the code to improve things later.