The issue happens when the Passport of the country you submitted to Uphold for KYC does not match the one you chose in Brave rewards.
For example, your passport is from India but you chose US since you shifted to US, there would be a mismatch. The brave back end checks the nationality through passport’s nation only.
You need to follow steps at
https://community.brave.com/t/psa-current-faq/464018/41