So I unlocked trade company HQ and now have the option to build it in all of my systems except one. Is there a placement restriction I don't know about, or is this a bug? 

Info: Unfallen, vaulters expansion, hard 6 player (5ai) random map setup. Image is comparing two systems (the one I can't build it in is on the left).

Isolated systems (not connected by wormholes or starlanes) can't build trade company HQ.

Ah, yep, that's it. Thanks!