I really don’t have any other suggestions. You might try to create a new profile, enable Brave Rewards, and see if the other custodial providers appear there. The link below provides instructions for creating a new profile. The post is talking about troubleshooting performance/memory issues but a new profile can also help when having setting conflicts and other issues that pop-up now and then.
Again, hopefully someone will pop in with other suggestions. You can always tag the moderators and ask for help. It is Monday here in the US so they should be back at work today.