I have a Xojo app which has xojo apps inside which run as helper apps. I have a complicated build system which builds the helper apps, then embeds them within the parent app.
Occasionally (perhaps one in 50 times?) I see this message for one of the helper apps.
I think it's some sort of timing bug - it's more likely to happen if I launch the app immediately after it's built, but it seems if I wait a while it almost never happens.
Perhaps the OS is doing some sort of background processing of the newly built app, and if that hasn't yet finished when you lauch it, boom?
macOS 10.12.6, various Xojo versions.