I've been having this issue too, can't get the mash calculator within a recipe to go back to metric after having it set and working that way for years. I've tried setting as imperial, saving and then setting back to metric and saving with no luck.
@Stu's-Brew@Paddy Fowler
We're still working on this, in the mean time I wanted to pass along a bandaid fix so it's not causing issues until a fix comes through.
If you open a new recipe, or an existing metric recipe, it'll switch to L/kg if you change the Units: at the top from Metric to US then back to Metric.
Sorry again for the issue, we'll get it resolved as soon as possible!