I use google calendar. Events are created and updated via the browser. The calendar feed is configured through settings/online accounts. I can see upcoming events in the calendar drop down. The calendar and desktop are configured for the same timezone, and alerts normally appear simultaneously on my phone and desktop.
I know sometimes stale calendar entries can be a factor, but I don't *think* that's an issue at this time (the change was made almost 24 hours ago, I don't see the API limit errors I used to see in logs).
ProblemType: Bug
DistroRelease: Ubuntu 20.10
Package: gnome-shell 3.38.2-1ubuntu1~20.10.1
ProcVersionSignature: Ubuntu 5.8.0-48.54-generic 5.8.18
Uname: Linux 5.8.0-48-generic x86_64
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair
ApportVersion: 2.20.11-0ubuntu50.5
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: ubuntu:GNOME
Date: Wed Apr 14 15:02:11 2021
DisplayManager: gdm3
InstallationDate: Installed on 2019-06-18 (666 days ago)
InstallationMedia: Ubuntu 19.04 "Disco Dingo" - Release amd64 (20190416)
ProcEnviron:
TERM=tmux-256color
PATH=(custom, no user)
XDG_RUNTIME_DIR=<set>
LANG=en_US.UTF-8
SHELL=/bin/bash
RebootRequiredPkgs:
linux-image-5.8.0-49-generic
linux-base
RelatedPackageVersions: mutter-common 3.38.2-1ubuntu1~20.10.1
SourcePackage: gnome-shell
UpgradeStatus: Upgraded to groovy on 2020-10-24 (171 days ago)
This is still happening in 21.04, most recently with a repeating calendar event instance that was canceled over a week ago. The desktop has been rebooted in the interim.