@karlenigma Netsuite's answer... "We have filed the following defect on your behalf. Defect 526300 : SuiteBuilder > Move a sublist to a Custom Subtab via Move Elements Between Subtabs > Custom Subtab is not showing after moving a sublist under it
Alternate Solution: Re-create the Custom Form.
After evaluation of the defect details, we’ve set the urgency level to U7. We currently do not intend to resolve this defect."