My '15 X Ltd will stumble if it heat-soaks. I'm not sure if it is also tied to fuel level. Not suggesting this is the fix, but I recently plugged the port for the OEM fuel pressure regulator and installed a remote FPR with a return line. The FPR is near the rear cylinder ignition coil, and the stumble (vapor lock?) is significantly reduced now that fuel is constantly circulating to that point and not absorbing as much heat. I have some heat sleeve tubing to add the next time I have the trunk out, and if I can afford to have my cylinder heads and turbo header ceramic coated, I may send the fuel distribution block I made to have it coated with a heat rejection coating.
Last year, my 'cat would heat-soak and die if it idled too long on a hot day. The fuel pump completely failed over the winter, so I suspect it wasn't making the proper psi when it would die. A new pump made it better, then the remote FPR improved it some more, but on today's ride it would stumble if we stopped for just a few minutes. Stopping for lunch lets it cool down completely, and the stumble does not happen.
When it does stumble, going WOT seems to allow the fuel pump to push the vapor through the injectors. It clears up and runs fine for a couple of seconds and repeats the stumble, then it runs fine. Probably because there is some air flow around the fuel lines at that point.