When you try to save your changes for EDI Agreement that use the EDIFACT/X12 encoding protocol settings, the changes are not saved. Additionally, you receive the following error message:
Unable to cast of type 'Microsoft.BizTalk.Administration.EdiExt.ComboItem' to type 'System.String'
The fix that resolves this issue is included in the following update for BizTalk Server:
Cumulative Update 5 for BizTalk Server 2016
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.