Comment 26 for bug 1766217

Have this same issue in 20.04 with xubuntu.
If launching via menu launcher - it runs with no parameters (update-manager) - and it reports that there are 400+MB of updates required, but I get no details of what they are.
If launching from shell with no-update parameter (update-manager --no-update) all is shown OK.

Using command line tools, there are presently NO security updates available, just non-security updates.

/var/lib/apt/extended_states_tmp has thousands of lines present (so I dont know which line is affecting behaviour here) - but if this file is moved aside - all works as expected.
Dont exactly know what purpose this file has (know what its for - but not what consequences of removing it are) so want to leave it in place.