Hi Christian,
I have prepared a sample that having more than 10 relations with GridGroupingControl. All the nested tables are displaying properly. Sample can be obtained from the following link:
http://www.syncfusion.com/uploads/redirect.aspx?&team=support&file=cs-17294553.zipPlease have a look at the above sample and if still the issue exists, could you please try reproducing it in the above sample or send us the reproducing steps so that we could sort out the cause of the issue and provide you a solution?
Regards,
Jisha