There is just one registrar -- the one under discussion. It's the main reason Kamailio is used here; it is the only OSS registrar I know of that has enough throughput capacity to sustain thousands of devices banging on it with relatively short re-registration intervals.
Hi Alex,
At this point I would consider customizing your script to append an extra header to your onreply_route logic using something like append_hf("P-hint: bla...bla...bla\r\n"). My guess is that a packet capture will show the header inserted under normal circumstances, but will be absent during the mystery registration in the 8 minute window. If that happens, it means your mystery registration is not hitting this server or its not following your expected logic in the config script.
Hope it helps.