I have narrowed it down to the Properties > Common > icon: which is causing this issue.
I came to this conclusion by having two icons, one named icon1.png and another icon2.png (both in the same folder “icon_splash”), then I selected icon1.png in Common and icon2.png in VoltBuilder.
Properties > Common > icon: icon1.png.
and
Properties > VoltBuilder > icon: icon2.png.
And VoltBuilder reports source path does not exist for “icon_splash/icon1.png”.
The last time I updated this app was back in 2024, so not sure what has changed.
I’m sure I had tried renaming the (top level) folder “icon_splash” to “icons” which had the icon.png file in it, but I was still getting the same error.
You also get similar error if you remove the image from Common > Icon, but it refers to the nsb default icon.
After you suggested removing <icon src="{icon}" /> from the config, I checked the config on another app, which is where I saw I had set the icon with <icon src='resources/iconTemplate.png' />, so I must have come across this before in the past.