Tools>Option>XAML Designer and enable XAML Designer worked for me.
PS: By default it is enabled. I disabled it due to VS performance issue and forgot about this change and end up facing same issue when I started working on WPF project.
XML designer can be disabled by Resharper in Resharper > Options > Performance Guide I fixed my problem by turning off Resharper block, and restoring XML designer in Tools > Options