Reproduction
Create a new C++ Actor class
Paste the following code in the BeginPlay function
Compile and place the Actor class in the level
Play in Editor (The result should be a crash)
TSharedPtr<SGridPanel> GridPanel;
SAssignNew(GridPanel, SGridPanel);
GridPanel->SetRowFill(2, 1.f);
Bug Source
SGridPanel::SetRowFill(…) uses an if statement instead of a while statement compared to SGridPanel::SetColumnFill(…) which doesn’t cause a crash.