Well, yes, the app Legend Slime (ID "com.loadcomplete.slimeidle") always spits out of Il2CppDecompiler:
System.InvalidOperationException: Sequence contains no matching element
at System.Linq.Enumerable.First[TSource](IEnumerable`1 source, Func`2 predicate)
at Il2CppDumper.Macho64.MapVATR(UInt64 addr) in C:\projects\il2cppdumper\Il2CppDumper\ExecutableFormats\Macho64.cs:line 71
at Il2CppDumper.SectionHelper.FindMetadataRegistrationV21() in C:\projects\il2cppdumper\Il2CppDumper\Utils\SectionHelper.cs:line 256
at Il2CppDumper.Macho64.PlusSearch(Int32 methodCount, Int32 typeDefinitionsCount, Int32 imageCount) in C:\projects\il2cppdumper\Il2CppDumper\ExecutableFormats\Macho64.cs:line 241
at Il2CppDumper.Program.Init(String il2cppPath, String metadataPath, Metadata& metadata, Il2Cpp& il2Cpp) in C:\projects\il2cppdumper\Il2CppDumper\Program.cs:line 213
ERROR: An error occurred while processing.
I figured it was a decryption error, since the version of the app I downloaded myself had the same exact UnityFramework bin in it (same size). But, if this isn't a decryption error, then I'm not sure why Il2Cpp is spitting this error. I tried both locally-run Il2Cpp and the online version of it.