SPFx header application customizer loading twice

[EA12]

What type of issue is this?

Question

What SharePoint development model, framework, SDK or API is this about?

💥 SharePoint Framework

Target SharePoint environment

SharePoint Online

What browser(s) / client(s) have you tested

• [ ] 💥 Internet Explorer
• [X] 💥 Microsoft Edge
• [ ] 💥 Google Chrome
• [ ] 💥 FireFox
• [ ] 💥 Safari
• [ ] mobile (iOS/iPadOS)
• [ ] mobile (Android)
• [ ] not applicable
• [ ] other (enter in the "Additional environment details" area below)

Additional environment details

• SPFx version 1.13.1

Issue description

This Application Customizer provides a global Navigation for each Site in a Tenant. This component is running in production since more than two years without any problems. From around 800 Sites, there is one (and only one!) Site which shows the global Navigation twice.

Anybody else stepped into that issue?

[EA12]

The responsible user for this Site added the Global Navigation App to the Site. - That's all. I have removed the App and everything is back to normal.