DaveW

Well, I think I’ve found out what it is, and (doh) it’s fairly obvious. I’ve got the Category Access plug-in installed and, of course, the feed can’t tell which categories it’s allowed to serve unless you’re logged in. With CA turned off, the feed works fine. Turn it back on and it chokes. (There is also confusion caused by cacheing somewhere up the chain, but I don’t think that’s anything to do with the root cause.)
Problem understood, if not solved.

Wait! My RSS reader (Sage) has started working again… And it seems to be because I added ‘?xxx’ to the end of wp-rss2.php in the feed properties. I think it’s a (bizarre) cacheing problem. There’s no other explanation for it. (Is there?)

New news. With no expectations, I updated to 2.0.2 and my Sage (Firefox) reader stopped seeing the RSS2 feed. However, a friend of mine tells me that his GreatNews reader has been able to read the feed since before I did the upgrade. Are we looking at a content-specific bug here? Are some of the reserved XML/RSS characters not being properly trapped? (It doesn’t explain why I can’t see anything other than the header, but that might be my reader too…)

Just an afterthought (but it might be worth checking) as the RSS container seems to be recognised ok by most readers, but the contained items aren’t, are they being written properly (RSS-compliant)?

I’ve just had this pointed out to me on our site too. I’ve been through several RSS readers (FeedReader, SharpReader, BlogBridge, Amphetadesk, and RSSOwl) and they all find the feed but with no items in it as gloddy reported at the top.
The feed on https://URL/?feed=rss works only if you type it into a browser (both IE and Firefox work) in that the items are shown, but in case it helps with the diagnostics, the FF RSS reader Sage is the only reader/aggregator I’ve found that finds the items. I don’t know what it’s doing differently, but it might provide a clue.
PS. I’m not using permalinks (I don’t think) so wouldn’t be affected by those.