Hello hammed,
Thank you for posting in Apple Support Communities. We understand that you are having trouble with the Pokemon Go app crashing and after removing and reinstalling it the health data for the tracker linked to the Pokemon Go app is empty. We would love to provide support on this. When you remove a third party app it deletes the associated data with the app is all removed. Even after reinstalling it the apps data that is connected to your health tracker is also removed with is why it displays no data.
The app developers might be able to help you address the issue that you're experiencing that causes you to have to delete and download the app again. Here is their support page: Pokemon Go Support
These resources will also help to manage your health app data:
Manage Health data on your iPhone, iPod touch, or Apple Watch
Use the Health app on your iPhone or iPod touch
Thank you for allowing our support community to help.
Have an awesome and productive day!