How do I avoid shutdown-inhibition caused by an interrupted, then completed, Ubuntu upgrade?

Question

When I try to suspend/reboot my Ubuntu 18.04, I get a dialog asking for a password:

"Authentication is required for suspending [respectively: rebooting] the system
while an application asked to inhibit it"

How do I avoid this?

This answer actually works for me. But that question involved shutdown-inhibition due to multiple users. In my case, the cause is an interrupted, then successfully completed, Ubuntu upgrade from 17.10. So there is probably some lock file, and ignoring lock files is dangerous, so I would like to understand what is happening first.

Data

1. (Here is one minute from my syslog. As seen there, I started the suspend process at 18:19:00, was asked and then gave the password. The laptop was suspended, and then I resumed it.)

2. lslocks shows dozens of ordinary application locks from Eclipse, Slack, Chrome, Firefox, Atom, and KeePassX. Other than that, there are these lines. Maybe the dpkg lock means something?

COMMAND PID TYPE SIZE MODE M START END PATH

lvmetad 322 POSIX WRITE 0 0 0 /run...

thermald 817 POSIX WRITE 0 0 0 /run...

cron 863 FLOCK WRITE 0 0 0 /run...

dpkg 24505 POSIX WRITE 0 0 0 /...

whoopsie 1651 FLOCK WRITE 0 0 0 /run/lock...

3. The command sudo lsof |grep dpkg shows this.