I also have problems with the header since the update. I’m using a child theme. My header since the update has completely messed up and changing any of the settings in Header menu does nothing at all. I’ve removed my quick CSS and emptied the cache but still the header is messed up.
Hoping for a solution ASAP.
OK, I’ve figured it out and it’s probably what is causing others issues. I am using a child theme and have made a few customisations to the header.php. I had to delete my current header.php (from my child theme) and add my customisations to the new header.php file that I copied into my child theme folder.