I have a Web Experience that, when loaded for the first time in a browser session, always displays the following pop-up:

The pop-up is generated by the browser and I must click 'OK' before I can continue. The Web Experience proceeds to function as usual; everything works fine, despite the pop-up. When I refresh the page, the pop-up doesn't reappear. It only reappears when closing the browser and then opening a new browser window.
I have examined the network traffic using the browser dev tools (F12) but couldn't find anything related to this message. I also examined many javascript files contained in the Web Experience that could be even remotely relevant to the 'map view', but couldn't find the source of this message.
System info:
- Tested with ArcGIS Experience Builder Developer Edition versions:
- Tested in the following browsers:
- Edge 136.0.3240.92
- Edge 137.0.3296.52
- Chrome 136.0.7103.114
- ArcGIS Enterprise 11.3
- Internet Information Services 10.0.20348.1 (where the Web Experience is hosted)
All of the versions mentioned above show this behavior. Has anyone seen this before? Any pointers would help me out. I just want to get rid of the (seemingly irrelevant) pop-up, as it hurts the user experience.
If it helps I can send a HAR file of the network traffic for if anyone wants to take a closer look.