On the Edge 830 and 520 (presumably all Edge devices), the firmware will change a manually set 'Max HR' if the User Profile 'weight' is changed. I assume this bug came about that whenever a user were to change other User Profile settings, 'birthdate' and 'height' that would mean it was a new user but that's just not the case with 'weight'. The 'Max HR' setting affects several other calculations such as 'calorie burn' and '% set HR zones', and it was frustrating getting odd calorie numbers before I realized what was causing the change for similar workouts.
Thanks for looking into this bug. Look forward to a fix.