Last week, I wrote on Twitter:

The (not yet announced) third app for #12M6A is coming along nicely. Probably can be submitted in the next 3-7 days!

Fast forward to today, exactly 7 days later: I haven't submitted the app yet. And it won't happen for a few weeks at least.

That's because there is an error in my Xcode 6 project (similar but not identical to: 1,2,3,4), which I was not able to resolve. Yesterday I rebuilt the entire project from scratch using the current Xcode 7 beta, received the same error at some point, but was able to resolve it using some of the steps from the above-linked Stack Overflow answers, which however didn't resolve the same error in Xcode 6 for some reason.

So I'll wait with submitting the app until Xcode 7 comes out of its beta status and it's possible to submit apps to the App Store with it, a few weeks before iOS 9 drops.
I could try to get it working in Xcode 6 further on, but I already wasted too many evenings on this problem and it's just not worth my time anymore.

Development for the app is almost completed, as is the creation of the other resources needed for its submission. I'll wrap it all up and just wait until it's possible to submit with Xcode 7 and then do so.
In the meantime I can already start working on the next project and won't lose any more time struggling with weird Xcode issues.

P.S.:
Because the release of iOS 9 is so close by and I have to wait for it (respectively Xcode 7) anyway, I'm now thinking about targeting iOS 9 instead of iOS 8. I was busy developing Viable and app #3 for iOS 8 since the new iOS 9 api's were introduced at WWDC and thus haven't looked much at the shiny new bits yet. That's another decision I'll make in the next few days.

Update: Someone cheered too soon. The problem came back after a few days in Xcode 7 as well. I'll take a look at it sometime soon, but for now this project is cancelled/deferred. Working on the next one already.