Broken syndication feeds are worse than no feed
Over the time I've been using syndication feeds a lot, I've had to deal with various sorts of feed problems. And I've come to a conclusion: broken feeds are usually worse than no feed at all.
Broken feeds invite you to trust them, but then betray that trust; you wind up doing extra work to make sure that you're actually seeing everything and what you're seeing is actually there. (Broken feeds are also frustrating; if only they weren't broken, they would be so useful. A shiny thing is being dangled in front of you that you can't have.)
Or to put it another way: if a site has no feed, at least I don't have to waste my time trying to use it and get annoyed at its problems.
So, if you've got an incomplete, erroneous feed, please do everyone a favour and shut it off (with a notice about it!) until you can make it work reliably. How can you detect that your feed's got problems? Well, let me suggest that you read your feed.
As a corollary: if you are going to shut down your feed or stop updating it while your site keeps going, please do put up a final entry in the feed about it. Don't assume that just removing your feed URL will be noticed by everyone, because there are any number of online feed reader interfaces that don't show that to the user.