Sorry, I'm at a loss on that one. Have you tried rebuilding it to test it out one component at a time?
Its a pain, but I had to do that recently to identify that a certain widget didn't like me pulling in the Imagery w/ Labels basemap individually and without having the ESRI basemap portal checked.
Initially the designer of the widget was unaware of the conflict and as to why they don't play well together. So far there was no solution so I had to remove the Imagery w/ Labels basemap and opt for just the Imagery. I don't like having an excessive amount of basemap options.
Point being, sometimes you have to rebuild the app, one component at a time and test it to find the potential bug that is not known to the designers. Good luck.