When user is banned, do not allow them to follow the streamer they are banned from.
When a user is banned, currently they can still follow the channel. Some trolls use this to get past mods who are removing game spoilers from the chat by following, as this often brings up alerts and non deletable messages in the chat with the spoiler. A example of this has been seen often in The Last of Us 2 streams where they spoil the ending. This has happened repeatedly on a stream I moderate, and across multiple others, pre-emptive banning to try and stop them does nothing to stop them following.
A simple fix in Twitch's code would be to not allow banned, and maybe timed out account, to join the raid.
People right now can manually not participate in the raid, and it seems simple to leave the banned account out of the raid.
A little extra code could make it that banned account can't even see the post-raid host details. The account would be left behind on the offline channel.
Banned viewers can use raids as an opportunity to do the things that got them banned from said channel.
Another idea to fix the suggestion I have is if someone gets banned, they will not be allowed to watch the stream either, and they cannot access the twitch channel page for said streamer.