A dot (.) – it is harmless. What harm can it do, it looks pretty innocent.
And yet it can break your Catalog UI.
Catalog UI relies on the Shell UI from CMS to render properties and such. Shell UI, in its hands, needs to know about the metadata of the properties. When you have dot in the metafield names, the MetaDataPropertyMapper will create an Property with that name on site start up. And then when you open All properties mode, Shell UI will request your content type models, and CMS Core will happily return those properties.