Saving JWT's in any medium is a security risk. The blacklist method needs to be stopped.

The most straightforward example one can give:

1. Hacker gains access to your database.
2. Hacker reads all invalidated tokens in the blacklist.
3. Hacker clears the blacklist. Now all blacklisted tokens are back to Active and Good state.
4. Hacker does bad things with the stolen, previously-blacklisted-but-not-anymore, list of tokens.