Unable to add members to a group

Hi Team,

We are facing an issue while trying to add child groups to a parent group either as a parent or members of the parent group. Either of the case it is not allowing. If we try adding forcefully, from other child groups it is getting deleted automatically. 

We are facing this issue when child groups are more than 25 to 30. One more issue we noticed is while adding a child group as a member, all its subgroups are getting added as a member internally. The child groups and their subgroups count is crossing 100 and after that, we are getting an error while trying to add.

Please help us by resolving the issue or providing the solution.

Currently, the parent group has 51 child groups and these child groups have 152 subgroups. 

Regards

Rajani