Health and Fitness apps steps sync

I have a question about how health and fitness apps work. My steps isn't always the same on the watch fitness app and iphone health app. I also checked that devices set priority is apple watch so everything should be right? Maybe it doesn't sync after when the watch is turned off and later toggled on again ?Or when I leave my watch and use the phone instead? Sometimes it's accurate but just usally when I wear the watch for the whole day.

Thank you for your answers <3