Custom Modules: Field name cannot be "css_class"
This is an error we get upon upgrading the old modules in the new design manager. Some field names aren't allowed to be use. (ex: body, css_class, Module_id, label, ...)
The module would still work but it won't allow to save any new updates until that field is removed/renamed. The issue here is that by renaming the field, all related data on pages will be lost.
"It would be awesome from HubSpot, for those particular fields, to keep their data when renamed."
This is really an headache when you have a certain naming convention applied on all the modules, then you need to pass by them all, on all pages, to recover the missing data.