Not having used Steam for about 2 months I fired it up after reading
your post and found that HL-2 and HL-2 episode 2 and 2 or 3 others where
marked as updating paused! I resumed them and now all current, I did
not pause anything so not sure why this happened.
Back to your problem, a few years ago I had similar problems and the
cure back then was to rename client registry.blob to client
registry.old, Exit steam and reboot and restart Steam and this file
would be recreated and all would work again.
I don't know if this still works but may be worth a try, If not you can
rename .old file back to .blob and be back where you are now, ( no
guarantees) hope this helps, let us know.
Regards Rene