If you have a GRID in the datatemplate (either in the group header or in the item) then the bindings will not work correctly. If you update a string value, then it does not update in the template, but rather gets set to an empty string.
If you wrap the Grid in a Stacklayout, it magically starts to work again.
I will attach a reproducer project, based on the Xamarin Forms Samples on github.
Created attachment 18462 [details]
Modified group list view from github
Uncomment the StackLayout in the .xaml file to see correct behaviour, re-comment to see bug
Which platform is this happening on?
Windows 8/8.1 and UWP
In the project (attached to this call) iOS and Android projects are also included, but i have not confirmed that the bug occurs in those environments.
This looks to be resolved as of the 126.96.36.199-nightly.