By default, if you import a wallet and then sync your node will be scanning all incoming blocks for transactions benefiting your wallet. However, that seems to not have happened in this case because your balance is not showing up. That points to a bug or to a discrepancy between how the tools were intended to be used and how they were actually used.
Either way, you need to activate scan mode while syncing. That’s the mechanism that will find your balance. Right now the only way is to sync from scratch and use either
--scan-blocks, or--scan-keys.
Going forward I will add to my todo list
- develop tools for rescanning blocks after sync has completed
- robustify scanning so it does not fail in the first place.