In many cases, interlink is often configured as an Aggregated Ethernet interface across multiple linecards for redundancy. 

When STP is configured on the interlink, failure of all child interfaces within a certain linecard may cause the STP block at the interlink, leading to service failure. 

When the customer removed all interfaces in one linecard for a redundancy test, a service failure occurred. It was restored right after restoring the interlinks back. 

In Junos devices, PPM(Periodic Packet Management) daemon is responsible for processing periodic packets such as STP BPDU, OSPF hello, VRRP hello, LACP hello. The process of PPM can be run in two modes: Centralized mode processes in Routing Engine, and Distributed mode processes in linecards. 

In EX9200, STP BPDUs are processed in distributed mode by default. When running PPM in distributed mode, the process decides which linecard will process the BPDU, and the selected linecard is called Anchor FPC. 

There is a known issue, PR1540380 , that when all links in the Anchor FPC go down, the BPDUs are not sent out anymore, causing STP topology change and possibly causing unwanted interfaces to get blocked.

You can take a look at the above PR for fixed-release information. 

If upgrading to the fixed release is not viable, you may change the PPM mode to centralized mode as a workaround.

set routing-options ppm no-delegate-processing