During a galactic war game on the Revenant boss (red faction leader) system I find that I can't place all catalysts on the metal planet. This is the system with one large metal planet with 3 small asteroid like moons orbiting it. This isn't because of any structures in it's way as any metal extractor close to it was destroyed and it's scraps removed yet the catalyst still couldn't be placed. Possibly the metal resource spots alone blocked the catalyst from being build? Rather weird seeing as other structures can be placed on top of metal resource spots without any problem. I'm not sure why this bug is still in the game.
I remember seeing a similar situation where the catalyst couldn't be positioned. The problem was caused by a prior build order to build a metal extractor there. Check your build queue. Maybe this is why there is a game setting to Always Show Build Preview?