Mystery event in hashtag stream

EventEmitter is choking on a weird event when listening to a "/api/v1/streaming/hashtag?tag=..." stream:

Mastodon::Listener: 1 at .../Role/EventEmitter.pm line 21.

This is on a Hometown server (v4.0.2+hometown-1.1.1) so I'm not sure if it has fun custom stuff or if it's just something new in v4 overall.