At DMEX we are continually working on improving the exchange and the user experience, therefore, periodically we are updating our contracts to allow this improvements.
When the contracts are updated, the balances will show up as Zero in the exchange header.
In order to withdraw funds form an old contract, please follow the steps below:
Go to Menu > Smart Contracts
In the first dropdown (Base Contract) select one of the previous contracts (the second one in most cases)
Go back to the exchange, you should now see the balance on your old contract.
Withdraw funds form the old contract using the standard Withdraw flow.
Switch back to the latest contract (using steps 1, 2, 3) and deposit funds to the new contract.