I submitted the issue on 30dec2024:
Case # 16208557: Hierarchical Instanced Static Mesh (HISM) not rendering in 5.5.1 until Editor UI is clicked has been received
“Thank you for your bug submission. We will review your case and will follow up if more information is needed or a ticket is created. In the event the issue you reported is scheduled for a future release or has known workarounds, you may not receive a follow-up message from our team.”
However, I haven’t yet received any other feedback or a tracking reference.
The only place I know about for reporting issues is in this “Issues and Bug Reporting” category, where we already are.