@DBreisch,
Not sure whats the reason behind this may be need to install the latest updates available for civil 3d 2020 and this fixes automatically.
What i can suggest you is instead of importing styles using command (IMPORTSTYLESANDSETTINGS) or through manage tab<<Styles Row, use reference template (command:ATTACHREFERENCETEMPLATE) method may be works for you.
Or else Enter Command LAYOUT and choose TEMPLATE option and choose your desired template or drawing file you want see the style, settings, expressions and etc.
Some time Reference template, drag and drop, import styles and setting dosnt function properly and i follow this LAYOUT method and it works good.
Some one had a similar issue and this post may helps you.
If this doesn't fix your issue feel free to share the file so that can check and find the resolution.
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Cheers,
Neil
Project Manager | Civil | ACE Inc.
Certified Civil 3d Professional | YouTube | My-Blog