Fix Battle.net "Blizzard Agent Went To Sleep" Error BLZBNTBNA00000005

I've been using Lutris to play some Blizzard games on my Ubuntu 18.04 desktop and I kept running into the same two issues over and over again. The issues are easy to fix, but not obvious, so I thought I'd share the fix with you in case you run into the same problems.

The first issue, and the most frequent one for me, is the Blizzard App Launcher (Battle.net) displaying a message that says "Blizzard agent went to sleep. Attempting to wake it up", with the BLZBNTBNA00000005 error code. Restarting Battle.net (and even the computer), trying to kill the Agent.exe process or every process related to Battle.net doesn't get rid of this issue on my system. I've been running into this issue quite frequently in the past few months.

The second issue occurs when a game has an update (it might be combined with Battle.net having an update in the same time and updating Battle.net first, but I'm not sure). In some cases, Battle.net gets stuck and refuses to install the update, displaying a "Waiting on another installation or update" message indefinitely, even though there is no other update available for either Battle.net or a game. Clicking the force update button doesn't solve this.