DO NOT store your seed on your pc or phone!
Use KeePass and store it on a USB drive or use a paper wallet.
iotas don’t just disappear. I’m in IOTA since 2015 and always know where my iotas are.
Either there was a snapshot and due to the display quirk of the wallet the balance was shown as 0.
-> In this case the iotas are still on the address and you just had to generate addresses.
Or there was a transition, and you had to do the Claim Process.
For technical noobs it’s just too early, they should store the iotas on exchanges. The experiencend users should store them in the wallet.