Hey Merijndk this is a current limitation in 7.4, I believe this will be addressed in 7.5.
BG properties will still go through to the machine and can be used in EBS etc, There is just not a nice way to add them into custom forms. I was told export the form and add in the properties then re import. I have yet to personally see that work correctly.
Can you help me understand what properties of Business Group were you using with OLD blueprints. I can check if we can get the same properties for Custom Forms.