Discourse forum hangs and times out, doesn't load

This has started happening again recently: takes several minutes for the forum to load.

Ping times to the DigitalOcean droplet are nominal: ~80ms. Server load is also nominal:

The timings in the debug thing in the corner (MiniProfiler) don’t reveal any problems: all times are within ~300ms:

(This page took about 3 minutes to load.)

Is there any part of the loading process between reaching the server and rendering the page that are not counted by the MiniProfiler?