XBMC playback of tvheadend recordings buffering

Recently, recordings that I've made with tvheadend have started buffering in my XBMC playback.

The tvheadend server is on the same machine as XBMC, so it's not a network issue.

I'm technically capable, but am a n00b when it comes to this stuff. Can anyone give me some ideas on how to troubleshoot this??