v1.6 Beta Runtime: Crash when runtime calls "lookUpMethod"

I don’t know if anyone on here is using the 1.6 runtime engine, but I might as well put it out there. I’m getting a couple of users testing my app that are getting crashes on startup every time. When I look at the crash on TestFlight, it gives me the following crash log:

#	Binary Image Name	Address	Symbol
0	StackIt	0x00237b62	testflight_backtrace
1	StackIt	0x002371fa	TFSignalHandler
2	libsystem_c.dylib	0x3af29d3a	_sigtramp
3	libobjc.A.dylib	0x3aab0fa4	lookUpMethod                        (one with the error)
4	libobjc.A.dylib	0x3aab21e6	class_respondsToSelector
5	CoreFoundation	0x32dba754	objectIsKindOfClass
6	CoreFoundation	0x32dba4a0	__handleUncaughtException
7	libobjc.A.dylib	0x3aab5a48	_ZL15_objc_terminatev
8	libc++abi.dylib	0x3a50211a	_ZL19safe_handler_callerPFvvE
9	libc++abi.dylib	0x3a5021b3	_ZSt9terminatev
10	libc++abi.dylib	0x3a50362a	__cxa_rethrow
11	libobjc.A.dylib	0x3aab59b4	objc_exception_rethrow
12	CoreFoundation	0x32d012a0	CFRunLoopRunSpecific
13	CoreFoundation	0x32d010c8	CFRunLoopRunInMode
14	GraphicsServices	0x368e033a	GSEventRunModal
15	UIKit	0x34c1d2b8	UIApplicationMain
16	StackIt	0x000e2616	main in main.m on Line 16
17	libdyld.dylib	0x3aee2b1f	start

If anyone could help, that’d be great.