When synchronization suddenly stops between Habitify and your Apple Health app, check the following steps:
Make sure Habitify can access your health data in the Settings of your Health App
Edit your habit > Goal > Logging method > Manual Logging > Erase Log, and save the change. Then, take the same steps but choose "Sync with Apple Health" again and save the change.
Manually log 1 value in your Health App, which can be 0. This is like a trigger to activate the synchronization.