Whenever the user delete an unused Virtual Network (VN) that is assigned to one or more connectivity templates (CT), these CT get unassigned from their ports even though they carry other VN in production.

This is quite dangerous as deleting an unused VN could cause a massive outage on all our ESX hypervisor sharing the same CT, which collectively host 1000s of VM on multiple production VN.

As Apstra release notes shows, this issue is a known behavior as AOS-44623/ESC-310 (Deleting Virtual Networks in CTs with Multiple VLANs - All Active Endpoints Unassigned), and the current workaround is to manually remove the specific VLAN from the CT before VN deletion.

RFE‑3417 has been logged to enhance the UX - by providing more context in the UI before deleting a CT. Engineering is targeting this enhancement in the Apstra 6.1.0 release. Please contact your Juniper SE/account team for more details about the RFE.