How to resolve Type Initialization Exception in Xamarin.iOS?

This exception occurs when the linker options is set to link all assemblies. As per the linker behavior, sometimes the linker will remove code that you might have called dynamically. In XlsIO.Portable, we have handled reflections, which causes the issue.  

We recommend to set the following argument in Additional mtouch arguments to skip the XlsIO.Portable from linking process. 

Example:  

Additional mtouch arguments: --linkskip=Syncfusion.XlsIO.Portable 

Screenshot: 

Alternative Way:

This can also be resolved by setting linker behavior option to Link framework SDK assemblies only.
  

Refer the below link for more information.

Xamarin Documentation link: 

https://developer.xamarin.com/guides/ios/advanced_topics/linker/