When you say you have updated to High Sierra...have you updated your Muse Application too through Creative Cloud too?
You may need to un-install Muse then re-download from Creative Cloud to get a clean build installed.
You shouldn‘t update to a new operating system, before the producer of your indispensable applications doesn‘t give you a go.
There are many glitches and problems with many Adobe applications (Illustrator, InDesign), which should definitely prevent any professional user to upgrade.
I think, up to now we have no guarantee, that Muse works well. The team didn‘t comment on this and I think, testing and investigating isn‘t finished yet.
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The team says that they have not noticed this behavior on Sierra. Would it be possible for you to upload just the portion of your file that is causing this issue and share the URL with us for investigation?