Mortgage interest rates move multiple times per day with the bond market. Agency loans (conventional, FHA, VA) price off mortgage-backed securities (MBS); jumbo prices off bank balance-sheet dynamics.
The rate you "lock" is the rate you close at — but a lock is time-limited (15, 30, 45, 60 days are common) and may carry a premium for longer periods. Floating a rate (not locking) is a bet rates will fall before close.
Never make a rate decision off a screenshot. Rates displayed on any static webpage are stale. Your broker should quote a real rate tied to your specific scenario at the moment of the conversation.