According to an internal memo there has been a change to the way thumbs are controlled. There was a limit per day before, but it appears that some users would use their red thumb limit every day and not go near the green thumbs. The overall red thumb to green thumb ratio was getting alarming so an extra constraint was imposed. At least if I read the memo right.
I don't think there's a limit the other way, green vs. red thumbs. The worst ratios I see for red to green with a quick look over different periods are around 10:1 (not Beersy, FYI), but there are plenty of people who post 10:1 green to red or more, I'm seeing some 20:1 over certain periods. Seems like overall we're more positive than negative, but people seem to react to the negative more than the positive...
Speaking of negative, I was in a toy shop on the weekend looking for a present for GreenNiece and noticed a certain character included in the "Villains" figurine playset...