Visio 2021 and still running in to the same bug!
The lower left corner is page position 0,0. It seems like Visio runs in to an error calculating the surface area of the shape and all its subshapes and ends up setting 0,0 and the lower corner position of the container, when there is a 1D connector in the group.
The problem with using just a line instead of a connector is a visual issue, connectors and lines render differently and do not properly align at some zoom levels, creating an ugly rendering. (we use Visio because its diagram rendering is so pretty after all!)
I can solve it with a workaround fortunately, just bypassing both bugs completely. But it would be much better if I could keep 1D connectors in the group, the workaround is not quite ideal.