Since it appears to be a problem with one specific article in the feed, as they say, it would help a lot to know what the feed URL is. Is this the blog, on the forum?
For reasons I can’t explain it’s now working again and I appear to have up to date posts. At time of writing the latest is “Taking custom tags from a page in the project” by @Vincent_Vincent timed at 12:35 UK time.
Okay, it could be that whatever content was causing the problem has rolled off the active feed list. The odd thing is that it is definitely declaring itself as UTF-8 encoded, and if I download the file raw and check it out, it appears to be arriving as a UTF-8 file as well.
Well, if you run into it again, let us know and I’ll be able to probably see the same thing.