Reproduction steps:
1. Open the attached project.
2. Go to "Build Settings > iOS > Player Settings > Other Settings > Configuration"
2.1. Toggle the "Allow 'unsafe' code" checkbox.
3. Build to iOS.
- Build fails.

Notes:
- Full error messages attached in the edit below.
- Disabling code stripping doesn't solve the issue.
- Pay attention to "Assets/CthData/NotifyData.cs" file:
= The issue can be worked around by changing:
...
Int16* i = (Int16*)&data;
string str =(*i).ToString();
i++;
return (*i).ToString() + "-" + str;
...

to

...
Int16* i = (Int16*)&data;
int a = *i;
string str = a.ToString();
i++;
a = *i;
return a.ToString() + "-" + str;
...

Reproduced with:
2018.3.0a1, 2018.2.0b6, 2018.1.2f1, 2017.4.4f1, 2017.1.4f1, 5.6.6f2
IL2CPP

Not reproducible with:
Mono