Turns out that the webwork2 directory and subdirectories, and in particular htdocs, had a mixture of files with some owned by wwadmin and some owned by root. This was most likely due to using sudo during previous upgrades. After changing all the file ownerships back to wwadmin, I was able to successfully run "npm install" in webwork2/htdocs and complete the 2.17 upgrade. Everything is running fine now, including the css.
Installation
css issues with 2.17 upgrade
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