Activity App vs Health App (incorrect)

Activity app steps say 20,000, but Health app states 24,000. On some days the steps are the same other days they are out by 4,000 steps. I do not understand why they are so different.

The other issue is I can look at yesterdays steps and they say X, a few days later I look at the same day and they are much higher

I do not understand which one is correct, and I do not believe this is happening for other people

I do not know which steps are accurate, for April so far the two apps are 86,000 steps different.

I have re-connected my watch to my iphone and this has made no difference

I am using an Apple Watch Series 3.

Thanks