I'm pretty sure that this is a bug. I have a Solution where I have configured a Control on a sub grid to display a Card form (custom entity). When I import the Solution (managed) into a clean environment I get the error systemform With Id = xxxxxxxxxxx Does Not Exist. The form that CDS thinks is missing is the Card form. I checked the Solution XML and that Card form with that ID definitely exists. To get the solution import to work, I had to remove the control from the subgrid and repeat the export/import process into the new environment.
Once the Solution is in the new environment, I had to go back to the source environment, add the control back on the subgrid and import the Solution into the new environment again. That worked.
Hope this helps anyone else who come across this issue.
Does anyone know how I get this logged on Microsoft's bug fix backlog?
Already got this issue with card forms and another component type that escapes me now. I'm sure you already tried, but have you lodged the support request from the Power Apps Admin Center? If MS acknowledges it as a defect, you'll have to explain with a set of questions (mini business case) why this defect is important to help them prioritize it in their backlog...