A rate hold expiring mid-search is a common and avoidable problem. If your search runs longer than expected, your agent should flag the expiration date early enough that you can renew the hold or requalify at a new rate before you are mid-negotiation on a specific house.
This matters even more once you have an accepted offer, since the gap between your offer date and your possession date needs to fit inside the remaining hold window, or your lender may requalify you at whatever rate is available on the day funding actually happens.
A rate hold is only useful protection if someone is watching the calendar alongside the house search. Get your hand-reviewed valuation from Joel Dyck.