It sounds like gnome-shell crashed, which will make everything freeze and the screen flash for a moment as it restarts. The apps keep running because Xorg is still running and never crashed. So...
Thank you for taking the time to report this bug and helping to make Ubuntu better. It sounds like some part of the system has crashed. To help us find the cause of the crash please follow these steps: 1. Look in /var/crash for crash files and if found run: ubuntu-bug YOURFILE.crash Then tell us the ID of the newly-created bug. 2. If step 1 failed then look at https://errors.ubuntu.com/user/ID where ID is the content of file /var/lib/whoopsie/whoopsie-id on the machine. Do you find any links to recent problems on that page? If so then please send the links to us. 3. If step 2 also failed then apply the workaround from bug 994921, reboot, reproduce the crash, and retry step 1. Please take care to avoid attaching .crash files to bugs as we are unable to process them as file attachments. It would also be a security risk for yourself. ** Changed in: gnome-shell (Ubuntu) Status: New => Incomplete -- You received this bug notification because you are a member of Desktop Packages, which is subscribed to gnome-shell in Ubuntu. https://bugs.launchpad.net/bugs/1891713 Title: I am unable to resize windows by clicking on the tops of them and dragging after gnome-shell restarted due to low performance. Status in gnome-shell package in Ubuntu: Incomplete Bug description: When I was saving a document, the computer froze, and so did the desktop, and mouse cursor. Eventually, the mouse cursor reset its position, and the screen flashed black but then back to normal. However, I was then unable to move windows around by clicking and dragging them. I had to manually minimize and then maximize the window back. This mostly happened to Visual Studio Code, which was running while I was saving data in another Java application. ProblemType: Bug DistroRelease: Ubuntu 20.04 Package: gnome-shell 3.36.4-1ubuntu1~20.04.1 ProcVersionSignature: Ubuntu 5.4.0-42.46-generic 5.4.44 Uname: Linux 5.4.0-42-generic x86_64 ApportVersion: 2.20.11-0ubuntu27.6 Architecture: amd64 CasperMD5CheckResult: skip CurrentDesktop: ubuntu:GNOME Date: Fri Aug 14 16:26:29 2020 DisplayManager: gdm3 InstallationDate: Installed on 2020-07-06 (39 days ago) InstallationMedia: Ubuntu 20.04 LTS "Focal Fossa" - Release amd64 (20200423) ProcEnviron: TERM=xterm-256color PATH=(custom, no user) XDG_RUNTIME_DIR=<set> LANG=en_US.UTF-8 SHELL=/bin/bash RelatedPackageVersions: mutter-common 3.36.3-0ubuntu0.20.04.1 SourcePackage: gnome-shell UpgradeStatus: No upgrade log present (probably fresh install) mtime.conffile..etc.apport.crashdb.conf: 2020-08-12T16:46:41.139091 To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/gnome-shell/+bug/1891713/+subscriptions -- Mailing list: https://launchpad.net/~desktop-packages Post to : desktop-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~desktop-packages More help : https://help.launchpad.net/ListHelp