Don’t know for sure but if it was me I’d leave it for a day or two at least and see if it sorts itself out. I’m sure your delegation will remain as-is meanwhile.
GD, This has happened a few times. Deleting the Testnet Wallet from your computer, redownloading the newest version, and restoring all your wallets again is a sure fix at leats on my Mac.
That said, the same thing happened just yesterday and I didn’t hav etim eto redo as described above, and it fixed itself.
regardless of when I fix it the rewards are always accurate so it seems like something local to a users computer.