how many addresses did you generate? (RECEIVE -> ATTACH TO TANGLE)
Maybe you need to generate more.
You will never loose one iota as long as you remember your seed.
Nothing really happened, this is how it works since 2015: After a snapshot, all transactions get deleted, and only the addresses with balances get saved. The wallet does not know which address belongs to you, until you generate that address. That’s why you have to re-generate all the addresses you had before the snapshot. This will be solved with the new stateful UCL wallet in the future.
Another possibility: You had iotas on a reused address (NEVER REUSE ADDRESSES!). If that is the case, a hacker could steal your iotas. That’s why the foundation sent all the iotas on addresses that where reused more than twice to a safe address.
Look for your address here: https://ipfs.io/ipfs/Qmeb4B5AEi5MWTreKPRtufBFRFWRVTpZkBpX6FeaXCAe3B
If it has the tag KEY_REUSE next to it, then it was affected.
In this case, wait for the next wallet version, it will containg a tool to claim back your iotas.