all about channel votes it's consistent and this is how it works

Channel vote what happens when you click thumbs Up or Down

Showing what it does Not saying this is how it should work it is how it works and is consistent.

If you are the first to down vote a video and you click Thumbs Down the vote count will NOT change.
If you click the Thumbs Up you will see the vote count goes Up

If another user had clicked Thumbs Down and now You click Thumbs Down the vote count will go Down by 1 vote.

I don't know and am not saying this means it takes 2 Thumbs Down votes for every click down.
Not saying it's a 2:1 ratio and Rumble is biased to show Up votes.
It is possible that's what Rumble is doing.