I did a test with default lavatory - oval.rfa using system-default template. I didn't have your problem.
In the default mechnical plan view, connect a pipe into the hot water, I got the warning " None of the created elements.........". The pipe disappeared. As I said before, I adjust the filter in the VG dialogue. check the domestic, the pipe can be seen again. Or I directly switch to 1- Plumbing view, the pipe is also there.
jade.l