I thought it might be helpful to anyone still having this problem (where the fix hasn't been backported yet) to mention that the workaround is described in Bug #1607535 (essentially, delete the affected partial download files in /var/lib/update-notifier/package-data-downloads/partial/ and then try reinstalling again).
I thought it might be helpful to anyone still having this problem (where the fix hasn't been backported yet) to mention that the workaround is described in Bug #1607535 (essentially, delete the affected partial download files in /var/lib/ update- notifier/ package- data-downloads/ partial/ and then try reinstalling again).