HR is not a super great measure as it can vary for so many different reasons - training load, hydration, heat, etc.
I personally find my HRMax can change by over 20bpm depending on varying factors. The largest factor for me is plasma/blood and stroke volume changes that come from heavy training loads. Aka, training heavy then suppressed HR. Doesn’t mean I’m fitter, it just means my heart is pushing more blood per beat.