Proxy contracts for Synthetix (SNX) and Synth USD (sUSD) have changed on May 10th. Any ETH wallets with balances for either token are incorrectly referencing the Legacy proxy contract which does not show the correct current balance. See here:
Hey! Contract addresses are updated. Please take a look and let us know in case of any concerns.
The new proxy seems to be added, but the old proxy is still active in the app, so both SNX balances in an ETH wallet are being counted. The old proxy needs to be removed in order to see the correct balance.