I tried both ionic as well as Framework7 and buttons gets added (looks like duplicates). This is in the latest version 3619 on Windows 10. I am not sure what the reason could be. Here are some captured images of UI. I believe they are duplicates as they have the same ID when a custom script is created. The DOM does not show two buttons but the properties and interactivity pages do.
I cannot reproduce this. When I insert a button with Ionic or Framework 7, I get only one entry in the Interactivity panel.
Have you created multiple pages? Maybe one of those other pages also has a button? Can you .zip and post your project?
Interesting, I see the problem. The extra div that has been added next to the button is causing the interactivity parser to add an extra entry. I'm not sure why - certainly, it shouldn't.
I'll log it. In the interim, just ignore it.
Note, that you put your x() function in the index_init_scripts.js file. I would recommend you put your own functions in your own .js file. Just keep the App Designer event handlers in that index_init_scripts.js file.