appindicator icons don't appear if they are enabled after the panel was started

It was noticed that applications that use AppIndicator won't have their icons shown if the application was started or enabled its icon after the panel startup. I'm using the systray from xfce4-panel. It shows as an external plugin, but the star that shows the credits isn't enabled.

Between the many application I tested, there is Steam, OBS Studio, psensor, modem-manager-gui, onboard, and a program I wrote that has both Tray Icon and AppIndicator: the AppIndicator of it does not show on xfce4-panel if enabled after the panel was (re)started.

ProblemType: Bug
DistroRelease: Ubuntu 22.04
Package: xfce4-panel 4.16.3-1
ProcVersionSignature: Ubuntu 5.13.0-19.19-generic 5.13.14
Uname: Linux 5.13.0-19-generic x86_64
ApportVersion: 2.20.11-0ubuntu73
Architecture: amd64
CasperMD5CheckResult: unknown
CurrentDesktop: XFCE
Date: Wed Nov 3 09:59:36 2021
InstallationDate: Installed on 2017-06-13 (1603 days ago)
InstallationMedia: Xubuntu 17.04 "Zesty Zapus" - Release amd64 (20170412)
SourcePackage: xfce4-panel
UpgradeStatus: Upgraded to jammy on 2019-12-22 (681 days ago)
modified.conffile..etc.cron.daily.apport: [deleted]