For Langify V1
langify adds hreflang tags as soon as you separate your languages by (sub)domains as described in this guide: Enabling the domain feature.
For Langify V2
In the new version, the hreflang tags are managed by Shopify. They are generated based on your Market Settings.
If you still have the code from v1 in the theme, there could be a conflict between the langify and the Shopify hreflang tags.
Please get in contact with the support at firstname.lastname@example.org
You can double-check your hreflang tags here.
This is how it should look like: