I've just started my first score mix for an Atmos feature film, working in Atmos Bed 7.1.2 format, in PT 2018.3 (I assume it was the same for previous versions, though have not checked). I'm running a single HDX card.
The issue: .7.0.2 and .Overhead subpaths don't work correctly on internal busses (but they do work on output busses). See the video:
(There's pink noise panned center overhead to a 7.1.2 bus routed into the main 7.1.2, working correctly, then it gets routed into the .7.0.2 subpath - it gets routed only to the left overhead channel, then panned to the .Overhead path - it gets routed to the L and C channels!)
Edit: Fixed the video link.