A few days ago there was a disruption in my feed distribution and, long story short, I discovered that my original feed was getting a "timed out (Server timed out; misconfigured server?)" error checking it through feedvalidator and so recent posts were not being updated. This seemed to affect the /feed and /feed/atom, but not /feed/rss (the only feed not timing out).
I deactivated all plugins and the feed validated. I reactivated one by one, checking the validator after reactivating each. After activating YARPP the feed time-out occurred. Just to double check, I deactivated all plugins, checked that the feed was validating, and then reactivated YARPP first. Same error, which is a shame because I've used the plugin without issue for a while now and I like it. If there's something I can try, I'd like to know but as of now, the plugin is deactivated. :(