For several reasons, closing the Snap Store (Ubuntu Software) window is not enough to close the program itself. Instead, it will be kept running in background.
To fully close it, just open it, do click in the “Ubuntu Software” text in the left part of the top bar (if your language isn’t English, it will be translated), and choose “Quit” (also translated). It will fully close the Snap Store and you will be able to update it using “sudo snap refresh snap-store”.
I was going to post something along this same line. I figured out how to end the snap store using the “System Monitor” application, but this is NOT something a beginning Linux user would instinctively know to do. You need to come up with a far more user friendly way to allow the Snap Store to be updated so a newbie isn’t nagged with those “you must close the snap store so it can be updated” (I know that’s not the actual wording) messages.
I tried this but it did not fully end the snap-store process, so I was not able to update it.
Before that I had tried a system reboot but to no avail it would seem.
I had to end the process (either through kill <snap-store processId> or using the system monitor app), and I was then able to run sudo snap refresh snap-store.
As @jaime-cruz states, a more user-friendly way of updating the snap-store would be very welcome.
Great advice, this quit also works for other apps that will tend to run in background. Fox emaple Rhythmbox or Feedreader. Both run in the background process to either play music or look for new articles/posts to his the RSS feeds respectively.
I hope it becomes the default. It wouldn’t do to have to start the snap store from the command line rather than have it start up automatically without it.
Users are still running into this three months later – do we need to visit every user and ask them to run manual commands to update? Or just hope we catch them at the next LTS upgrade cycle?