It seems that if you upgrade an improvement with a placement limit of 1, with an improvement that isn't an assigned auto-upgrade, it then becomes unavailable to that planet. Until you reload your game. Sometimes.

Bug?

Also the AI doesn't really like improvements with placement limits it seems, which may explain its reluctance to build the standard orbital logistics thingy. Not only in my mod, but in the original game, the AI sticks to the same core buildings. Is there a way to get the AI to be a bit more diverse? My mod has a number of additional improvements with a placement limit of 1 and the AI very rarely builds any of them. Which is a shame, because these are the fun ones to have upgraded as you progress through the tech tree. Plus lots of placement limits means lots of interesting improvements and much more "fun", characterful planets. And it makes specialising planets enjoyable too.

Any input welcome (sorry went all Yor there).