In version 4.12, there is a bug where the height and weight appear to be 0 in the update height and weight section. This bug appears for users who have not accepted the apple health weight permission.
The bug will be fixed in version 4.13. For now, there are the following workarounds:
A) Turn on the weight permission by going to apple health -> sources -> stryd -> weight
B) Update the weight manually by turning the dials and pressing update. Note that in this version of the workaround you will still get 0s when you return to this screen, but know that your height and weight were updated to your new values.
You can read about it in detail here:
This is only a UI bug, and the weight and height on your device have not been changed to 0 (unless you press update while those values are 0 on screen). For now, you can manually change the height and weight and press update, or you can turn on the weight permission with Apple Health and update your weight there.