Inaccurate tracking on Watch series 4

Have you calibrated your watch by walking on a flat surface for 20 minutes at a consistent pace?

It is a bad idea to compare different tracking devices with each other, unless you have used professional level equipment you have no idea which one is accurate. This is especially true for step counting (which Apple pretty much deprecates).

Does your Fitbit include a GPS unit? If not then your Watch, unless it is malfunctioning, is probably much more accurate regarding the distance you have traveled. As far as the Activity circle, for it to record you need to be doing the equivalent of a brisk walk, or roughly 75 - 80% of your maximum heart rate. If you drop below this it will not count as Activity time but it still will record your move calories, distance traveled, time of your walk, steps, etc. Be sure in the Health app you have entered all of your demographics.

If you are taking medication that keeps your heart rate lower it will be more difficult to move the Activity ring.

Hi!

Read this :)

https://support.apple.com/sl-si/HT204516

check these settings