Edit

Field gets auto-generated InternalName in a list

Problem

While adding field directly to a list via .AddField() syntax, target field gets auto-generated InternalName.

Explanation

By default SharePoint would generate InternalName for a list scoped fields. That can be controlled via Field.AddFieldOptions property.

Solution

While adding field directly to a list FieldDefinition.AddFieldOption should be set to "AddFieldInternalNameHint" so that field would get the right internal name within a list.