Guided Landed Pages showing errors on approval

I'm using guided landing pages and have been previewing and publishing them ok. Suddenly on one set of templates after re-editing and approving them the css file (which is stored in Marketo and is a Marketo link) is not being pulled through and replaced with what looks like an auto generated url. Is this a Marketo bug? Nothing has been changed within the Marketo templates which were working but now suddenly aren't.