Similar ERROR in /var/log/syslog for me on Ubuntu 20.10 with gnome-shell 3.38.1-1ubuntu1.1. Similar to comment #9 I have firefox with many tabs and dissenter (brave fork) with many tabs open.
Jan 4 06:43:29 desktop01 gnome-shell[2096000]: JS ERROR: TypeError: null has no properties#012_onFocusChanged@resource:///org/gnome/shell/ui/closeDialog.js:135:9 Jan 4 06:43:30 desktop01 gnome-shell[2096000]: message repeated 35862 times: [ JS ERROR: TypeError: null has no properties#012_onFocusChanged@resource:///org/gnome/shell/ui/closeDialog.js:135:9] Jan 4 06:43:30 desktop01 gnome-shell[2096000]: JS ERROR: TypeError: windowActor is null#012_addWindowEffect@resource:///org/gnome/shell/ui/closeDialog.js:90:28#012vfunc_show@resource:///org/gnome/shell/ui/closeDialog.js:162:14 ➜ ~ inxi -SMCG System: Host: desktop01 Kernel: 5.8.0-33-generic x86_64 bits: 64 Desktop: N/A Distro: Ubuntu 20.10 (Groovy Gorilla) Machine: Type: Desktop System: ASUS product: All Series v: N/A serial: <superuser/root required> Mobo: ASUSTeK model: X99-A v: Rev 1.xx serial: <superuser/root required> UEFI: American Megatrends v: 4101 date: 07/10/2019 CPU: Info: 6-Core model: Intel Core i7-5820K bits: 64 type: MT MCP L2 cache: 15.0 MiB Speed: 1765 MHz min/max: 1200/3600 MHz Core speeds (MHz): 1: 1626 2: 1243 3: 1387 4: 1291 5: 1379 6: 1316 7: 1329 8: 1300 9: 1288 10: 1247 11: 1356 12: 1282 Graphics: Device-1: NVIDIA GK208B [GeForce GT 710] driver: nvidia v: 455.38 Display: x11 server: X.Org 1.20.9 driver: nvidia unloaded: fbdev,modesetting,nouveau,vesa resolution: 1: 2560x1080~60Hz 2: 1680x1050~60Hz OpenGL: renderer: GeForce GT 710/PCIe/SSE2 v: 4.6.0 NVIDIA 455.38 -- 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/1880405 Title: High CPU and journal flooded with: JS ERROR: TypeError: null has no properties _onFocusChanged@resource:///org/gnome/shell/ui/closeDialog.js:135:9 Status in GNOME Shell: Unknown Status in gnome-shell package in Ubuntu: Triaged Bug description: O.k. it is an old Lenovo thinkpad T410. However, in 18.04, 19.04 and 19.10 I did face these problems. The sometimes I have to wait 10 seconds to see if a window reacts or not. It is hard to use. Installiert: 3.36.1-5ubuntu2 Installationskandidat: 3.36.2-1ubuntu1~20.04.1 Versionstabelle: 3.36.2-1ubuntu1~20.04.1 500 500 http://it.archive.ubuntu.com/ubuntu focal-updates/main amd64 Packages *** 3.36.1-5ubuntu2 100 100 /var/lib/dpkg/status 3.36.1-5ubuntu1 500 500 http://it.archive.ubuntu.com/ubuntu focal/main amd64 Packages ProblemType: Bug DistroRelease: Ubuntu 20.04 Package: gnome-shell 3.36.1-5ubuntu2 ProcVersionSignature: Ubuntu 5.4.0-29.33-generic 5.4.30 Uname: Linux 5.4.0-29-generic x86_64 ApportVersion: 2.20.11-0ubuntu27 Architecture: amd64 CasperMD5CheckResult: skip CurrentDesktop: GNOME-Classic:GNOME Date: Sun May 24 15:43:34 2020 DisplayManager: gdm3 InstallationDate: Installed on 2020-02-05 (109 days ago) InstallationMedia: Ubuntu 19.04 "Disco Dingo" - Release amd64 (20190416) RelatedPackageVersions: mutter-common 3.36.2-1ubuntu1~20.04.1 SourcePackage: gnome-shell UpgradeStatus: Upgraded to focal on 2020-05-08 (15 days ago) To manage notifications about this bug go to: https://bugs.launchpad.net/gnome-shell/+bug/1880405/+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