I am not sure if I understand you correctly. Did the AppBuilder templates disappear or you are talking about different kind of templates? I cannot reproduce such issue, however, I would ask you to verify if you are using the latest version of the extension for Visual Studio. You can check the version from inside Visual Studio - select AppBuilder
from the top menu, then Help
. Currently, the latest version is 2017.3.1012.3. You can also try to Clear the Local Cache and Cookies for the Visual Studio extension
If none of the above is helpful, to investigate this further, I would ask you to share additional details regarding the issue.