The configured value for numberfield (field generally) is not used when at least one of the properties (jcr:lastModified and jcr:created) are missing
the problem occurs when you have a fixed component with numberfield in a page. the min, max and value properties are configured. if the edit-dialog is opened, the configured value is not displayed.
but if you add the component in a parsys (jcr:created & jcr:lastModified are available) and open the edit-dialog, the configured value is displayed
i cannot reproduce the problem in AEM 6.3 (not sure which AEM version you are using).
anyway wcm.io inherites from the OOTB Granite UI number field and only adds a hidden @TypeHint to the field - all other functionality including the min/max feature is inherited from AEM itself.
so if there is a problem in this area, it's unlikely the source is in the wcm.io code. to be sure replace the wcm.io NumberField resource type with the AEM NumberField resource type and check if the problem is still there - if yes we cannot do anything about in wcm.io.