Please refer to this old discussion here in the forums: Post #16 in Things changed or removed between 1.3 and 2.0 and not found in Changelog
It seems this one and a lot more things didn't get in the changelog between 1.x to 2.x, it was maybe the biggest change Ext.NET ever had (before maybe, upcoming version 6 in ASP.NET Core). Anyway, that forum thread covered some of these comprehensively.
And remember, forums search is your friend. In this case I just searched for
in google, and the right thread was the second one. This may save you some time waiting for answers as the migration between Ext.NET 1.x to 2.x had the most changes and was largely discussed throughout the forums. Most of the issues you may face may be already responded.
Hope this helps!