I opened a wallet on blockchain.info in 2016 and i received some btc to an address from the request tab (not imported).
if you opened it early 2016, you may have a legacy wallet and that address isn't recoverable by the seed phrase
did you get the seed phrase since you opened the account, or sometime after (wallet upgrade)?
I don't understand how the address is located in my wallet in the used address tab but the balance doesn't show.
used or archived address tab? if archived, move it out of that tab and see if the balance/wallet reupdated correctly
and if it is part of legacy wallet, you should be able to extract its private key individually
can you post a screenshot showing the address (where it is located) in your wallet? you can blur sensitive info if needed