At least  I think.

It's sort of hard to tell due to the unique setup of my systems, which currently ALL have a trade HQ or subsidiary except one (which is also unconnected).

My 5th HQ was built on one of the unconnected systems and it claims I don't have a subsidiary, but I'm positive I built one.  Further the one unconnected system that doesn't have a subsidiary won't let me build one so maybe it's an issue with how I built the last subsidiary or because i got the "two extra subsidiary" tech before the 5th HQ.  Dunno.

Either way it's a little annoying.

I agree that's a nuisance, especially since unconnected systems often have interesting strategic and luxury resources that trade would benefit from.

Trade ships should learn to use their hyperdrives !