Both of our primary BIML developers are experiencing this issue with VS2017 after an update to VS2017. I have also tried the recommended trouble shooting steps listed above including the complete uninstall with Registry key reset and there was no change in behavior. I also completely re-installed Visual Studio and that also didn't change the result. Current work around is to make and save changes in a different text editor, such as Notepad++. Would really prefer to be able to use BIML Express as intended.