@linnx88: On a wild guess, I'd say you somehow ended up with newsfeed built in KF8 (AZW3) by Calibre... What's your default/preferred output format?
If it's AZW3, it should automatically fallback to MOBI, but if you have, in the MOBI output settings, the mobi file type option set to 'both' (mobi7+KF8) or 'new' (KF8) instead of 'old', I'm not quite sure what happens, and you may very well end up with a KF8 file. Which doesn't work for periodicals (and isn't supposed to, FWIW)
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