wireshark will prove if the event is coming from the pubsub server and Plex Media Server is not picking it up straightaway
I have actually found what might the problem here. I have found that we have transient deadlocks in Plex Media Server that hold up requests for up to 2 minutes leading to plex client apps timing out and I believe also the pubsub server events not being processed when they arrive.
we can prove it is the cause of the delayed pubsub server evetns with wireshark +corresponding logs
The forum threads posts where I investigated the issue that I have identified as transient deadlocks are