it could be a localisation thing, for example in the UK and US ', ’ is a 1000’s delimiter and ‘.’ is a decimal - is the locales on each device the same?
I had to change the format of the weight value, which my shortcuts asks for, in the shortcut from “number” to “text”. Now the value is showing as xx,x kg in the Health app again.
Doesn’t make sense to me to record a weight value as text… looks like Apple has changed something behind the scenes.