Anti-Robot Check Failed

When I try to do some things, like enter a giveaway, I get this window pop up that just says "Anti-Robot Check Failed", with no additional info. What does it want from me?

For example, I click Enter Giveaway. Then there's a slider at the bottom which enables the Enter Giveaway button. I press it. Anti-Robot check fail window pops up. All I can do is go back, refresh, and try again. Sometimes it works.

Tried different browsers, like Firefox, Edge, Chrome, but I just get the same thing. Am I missing something obvious here?