So. Apple released thier update to version 10 of iOS yesterday. Fundamentally, nothing has really changed 'under the hood' concerning Awesome Ultrasound Simulator, so no issues were to expect. However when using two devices running different versions of iOS (9,10), connecting can sometimes time out. I've seen issues when using the iOS 9 as remote with iOS 10 as monitor, but flipping the roles; iOS 10 as remote and iOS 9 as monitor works well.
After upgrading all devices to iOS 10, connection was again almost immediate and worked both ways.
Why this is happening, I don't know. I'll investigate and hopefully work out a fix. Until then my recommendation is to either stay with iOS 9 on all devices, or upgrade everything to iOS 10.