Locked guidelines are not in the UFO3 specification, and when the file is exported to UFO3 it breaks many UFO authoring and production tools. The offending code is <key>locked</key><true/>. When unlocking the guides, exports work fine again.
What version of Glyphs do you have? This should be fixed since the end of last year.
Yep, turns out I was working with files from old versions. Have asked to upgrade.