I run self hosted WordPress sites, like this one, and was performing the update to 6.4.2 and the first site went fine and all the remaining sites failed a manual update.
The error message was:
“Could not copy file.: wordpress/wp-admin/includes/update-core.php
Installation failed.”
I vaguely recalled that occasionally problems happened and downloads are partially stuck and the files need to be cleaned out. Yup, found the wp-content/upgrade folder and cleaned out the partial upgrade file and each site upgraded fine.
I would imagine somehow the file and/or its check failed and stored in a queue somewhere and by the time I got it again, I was getting a clean copy. No idea if it was on my machine or the WordPress server. Oh well