Nobody plans to lose a domain. It happens because the reminder went to an address nobody reads any more.

The notice goes to the registrant email

Not to the account you sign in with, and not to whoever pays the invoice. When those are three different addresses, only one of them is warned, and it is usually the oldest one.

Auto-renew is not a guarantee

It fails on an expired card, a declined payment, or a price change you never approved. The domain lapses either way. The difference is that you were sure it would not.

The grace period is not free time

Most gTLDs allow roughly thirty days of redemption after expiry, at a redemption fee that is often several times the renewal price. A domain recovered on day 25 costs real money.

What works

Keep the expiry date somewhere that is not the registrar's own inbox, and check it against the registry rather than against a spreadsheet you last touched a year ago.