weird behavior upon opening a session from someone else in PT12

[Inglesworth]

Brand new Pro Tools System. Brand New Mac Pro coffee can running OS 10.11, in a Sonnet chassis, running HDX2, and PT12.4.

So we regularly have editors/sound designers who sent sessions over to us for mix. One in particular is on an ancient PT rig (not sure exactly what version, but he still uses .ptf files, so somewhere between 7-9).

He sent us 2 sessions for mix today. Our mixer regularly opens them up and gets them ready to import to his mix template. One of them opened fine.

The other, opened with all of the outputs set to "no output". Because of this, we lost all of the sound designer's pan automation. When we set the outputs of the tracks, they all look double bussed (the "+" shows up next to the output). However, they are not going to 2 different outputs or busses, but the output we selected is listed twice?

The sound designer downloaded the session file he sent us to open it and check it on his system again, and everything looks right on his end.

We somehow managed to get the tracks single-bussed to the output, then did a save as, imported session data, and imported all of the pan automation from his original session, and finally back in business...

Until we save/close that session, and open up the mix template and import the sound designer's tracks into there from the session we just saved. None of the clips and media actually get imported into the mix template. We have checked the drop-down menu in the import session data window and it is set to import all of the data. Volume automation, pan automation, etc. all gets imported. But none of the clips show up on the tracks.

Any ideas out there on this one?