lemmy currently only sends one activity per receiving instance at a time, so there is a round trip for every single post, comment, vote, etc., before the next activity will be sent. you wouldn’t see any increased number of connections, as there’s only a single one.

do you have access logs for /inbox with the lemmy.world’s user agent? you might be able to derive some information from that if requests increased over time or something, maybe also response status codes?