I went and read the rules and I came across the unpredictable mechanics section and came across these roles being banned in games.
I very much disagree with this. I can understand the death miller part a bit as this is a rather fresh mafia community and something like that might be too early but I really don't see a problem with the jesters.
An endgaming jester won't work for a large game but is fine for a really small one and one can easily just have multiple jesters where all of them have to be lynched so it ends the game for a large game setting. Not just that, could add more mechanics to it if you wanna get real creative.
Really ain't seeing the issue with a kill immune and invest immune jester. The kill immune helps them out as it can be a struggle to get town to lynch you instead of night kill you and the invest immune gives them a challenge as well as they gotta go up against appearing innocent to a cop meaning they have to play a top level game here as being investigated innocent is almost a confirmation that you're town in a lot of games.