I was searching for answer and see this post and found that last answer with 3 downvotes looks disable.
is there any limit define for it? i have not seen this before. see below screenshot.
The answer element in the dom has the class
downvoted-answer. I don't know exactly what the downvote limit is in order to get this class, but you can try to check if it's -3, by upvoting it (to get it to -2), refresh the page to see if it's still greyed out then retract your upvote.
If nothing changes when you refresh the page it means the limit is -2 or -1. So you can find a -2 post and try the same thing.
If something changes it means the limit is -3.
I just tested myself because you made me curious and apparently the limit is -3.