I'm using the Mac wallet v188.8.131.52. I decided to test importing my private key while fully synced (another wallet address with nothing in it). I was expecting my balance to show right away as the chain was fully synced, but nothing happened. I restarted the app a few times with no luck. Restoring with wallet.dat worked. I also tried restoring with the privkey again, but from a fresh install (complete resync). This worked. Just posting for reference if anyone else comes across this issue.