I use the VS Professional 2019 Version 16.7.7 and the latest Xamarin.Forms. Working only with Android part on Windows 10.
I have the simple blank app with one MainPage and MainViewModel, where the viewmodels' part is implemented as separate assembly. In the ctor of viewmodel I initialize test string, which show on UI via Binding.
And the issue in the next: when I start application at first time - everything is OK, but when I change some code in the ViewModels assembly (for example - change test string value) and relaunch nothing happen. Application apply these changes only after clean/rebuild the whole solution. At the breakpoint we can see the old property value.
I've uploaded the sample to the Google Drive, if someone want to try to reproduce issue