I've occasionally had similar start up issues with iSem as AU. Not in GB but in midiSteps and modStep. I've never had project totally fail to open though—usually they crash on start up but then the next time, it opens ok. Some of this might be down to GB implementation. Some is probably due to iSem being a very early iOS AU instrument adopter*—it's possible some of the APIs have changed.
The tricky thing with support and Arturia's iOS apps is that they've hired external iOS developers to port them from the desktop. Rolf of nLog music did iSem and iSpark. Retronyms did iMini and iProhpet. If you're still having this problem, I'd try posting on the Audiobus forum. Seems to be the most active pool of iOS music knowledge out there. Not sure if he provides direct support but you might also try contacting NLog/Rolf via email or twitter.
* Rolf's apps have always been ahead of the curve on iOS music technology. I don't know this for sure but I have a feeling that he decided to create the AU version of iSem because he was personally interested in seeing what was up with the technology. Not because Arturia asked him to. As such, there might not be contract dollars in place to fix any issues related to it. That's 10000% speculation.
