Some SSE connections disconnected and reconnected every 30s

For most of the production cluster, between 13:05 and 14:02 UTC on 2024-10-01, a small proportion of SSE connections were disconnected 30 seconds after establishing a connection. For the duration of that 30s they still worked fine, and connection resumption was working correctly, so this should not have caused any missed messages. The net effect would have been a small increase in subscribe latency about once every 30s. Only the SSE endpoint was affected; websocket traffic (including anyone using an Ably SDK) was not. For customers connected to ap-southeast-2 (Sydney), the duration of the effect was much longer, between 10:06 on 2024-09-30 to 14:02 on 2024-10-01.