There's a rate limit that one can only expand one entry in a given user's All actions subtab per second.
In the previous (prior to November 2021) user profile layout, attempting to exceed this rate limit would result in a nice error message that clearly explains the situation:
You may only load 1 revision every second
However, today, with the new design, attempting to expand more than one entry every second simply shows a generic error message "Request failed", with no explanation of what exactly went wrong:
Additionally, the style of that message looks the same as the text that shows up if successful, so it may seem like the user added in the text "Request failed" to the post, which is not so. It's not initially immediately clear that that's an error message.
Can the error message please continue pointing to the real reason why the request is failing, that the rate limit is being exceeded, as it did before? Also, can the style please be changed to make it clearer that it's an error message?