/events URL returns no content in 0.31.0

We have just upgraded to 0.31.0 from 0.26.0 to pick up the recent GitHub API change.

The installation runs fine for several hours but then all requests will start timing out

It appears to be because an unbounded number of Pubsubstub connections are being created. I see many repeated events of the form

Feb 19 03:36:14 ip-172-31-37-230 env[1235]: I, [2020-02-19T03:36:14.855652 #1709]  INFO -- : [Pubsubstub::Subscription] Connecting client #7815470111917132360 (stack.1)

followed by an ever-growing number of repeated events of the form

Feb 19 03:39:19 ip-172-31-37-230 env[1235]: D, [2020-02-19T03:39:19.247287 #1728] DEBUG -- : [Pubsubstub::Subscription] Sending event #1582083559247 to client #7268750048476322816

This appears to be because the requests to /events?channels%5B%5D=stack.1 hang and return no content. In 0.26.0 the requests return content of the form:

id: 1582083655404
event: heartbeat
retry: 10000
data: ping

Reverting to 0.26.0 appears to fix the issue

Please let me know if I can provide any additional information to help diagnose the issue

Start by reproducing the /events?channels%5B%5D=stack.1 request and comparing its response with 0.26.0, then trace the Pubsubstub subscription behavior described in the logs. Done means /events returns heartbeat content and repeated requests no longer create an unbounded number of connections.