Why is Update Manager getting stuck unless I hit 'q'?

Solution 1:

apt-listchanges is a package that does exactly what you describe:

apt-listchanges is a tool to show what has been changed in a new version of a package, as compared to the version currently installed on the system. It does this by extracting the relevant entries from the changelog file, and the NEWS files.

It can be run on several .deb archives at a time to get a list of all of the changes that would be effected by installing or upgrading a group of packages. It can be configured to do this automatically during upgrades using apt.

This package has probably been installed on your system. If you don't want this behaviour, remove the package or change the configuration.