To reproduce:
1. Open new project
2. Set build target to iOS
3. Set scripting backend to Mono 2x
4. Set Stripping level to anything other than "Disabled"
5. Build and open in XCode
6. Try building to device
Notice that there are errors:
"RegisterMonoModules.cpp
/IOS Build/Libraries/RegisterMonoModules.cpp:4090:16: Use of undeclared identifier 'Unity' (line 4090 RegisterMonoModules.cpp )
/IOS Build/Libraries/RegisterMonoModules.cpp:4097:16: Use of undeclared identifier 'UI' (line 4097 RegisterMonoModules.cpp )"

Reproduced on: 5.5.0b1, 5.5.0f2, 5.5.0p3, 5.6.0b1
Not reproduced on: 5.4.3f1, 5.6.0b2