When players are banned for spammy usernames (or other reasons), particularly early in the wipe, they can/will appear in leaderboards.

Would be great to see an option to facilitate excluding them

Until this suggestion is implemented, you can manually remove the entries from the data\challenge_data.json file while the mod in unloaded and then send it back and load the mod.

Use JSON Lint to check your config, if you need to.