Comment 22 for bug 894671

The main issue most have with U-M is it will eventually work if they wait it out, can take from 2-12 min, around 5 min. here.
Then it will work once & the 'wait it out' will begin again, whether trying to install another package or update the cache.

This started several weeks ago, before Alpha 1.

It would seem aptdaemon is involved, if you remove aptdaemon then U-M open promptly, updates the cache if asked & installs packages quickly & with no issue.
After installing a package(s) it will then crash but that's not too relevant, I'd assume U-M is setup to run with aptdaemon installed.
(this would be the crash with aptdaemon not installed - Bug 724687