However I get the exception below in my release build. What fixed it for me was adding this flags as additional mtouch arguments. Otherwise, I'd get a fatal exception:
-optimize=-remove-dynamic-registrar flag to MTouchExtraArgs
I suspect the simple act of instantiating SFBusyIndicatorRenderer alone without assigning it does not preserve it? Perhaps you could add this to a future release as SfBusyIndicatorRenderer.Init() to also be consistent with all other syncfusion controls.
SIGABRT: Can't register the class Syncfusion.SfBusyIndicator.iOS.SfBusyIndicator when the dynamic registrar has been linked away.