Can you tell us a bit more about the issue? Is your estimated earnings changing, or the actual wallet balance? Estimated Earnings are shown on the New Tab Page, whereas Wallet Balance can be found in the purple region of brave://rewards. Also, which version of Brave are you presently using?
Please also check to see whether you have Automatic Contributions enabled on brave://rewards, or have issued tips to other users (these will be shown when you scroll down to the bottom of the aforementioned page).