In my case it was due to a plugin having some invalid CSS.
I would recommend going through each plugin if your site has any and seeing if any are causing the issue.
I also noticed there being a difference in behaviour between two environments, but one thing I found to be more true for live was setting the Umbraco:CMS:Hosting:Debug setting to false ( Runtime minification settings | Umbraco CMS), this ensures Smidge bundles as it should for live environments. With it being true, the issue was not occurring as it was more forgiving, which explains the difference.
Hope this helps.