Are you able to share a link to your site? Without it it’ll be quite hard to troubleshoot.
Some changes were made to the way the header works in a recent Discourse update. Even if you don’t have a custom theme for the header itself, it’s possible an unrelated theme has some CSS impacting it.
It seems that deleting and reinstalling a theme component did the trick. Not sure why a reinstall fixed it (already updated) but I’ve learn not to question certain things. Thanks for the support!