Fallen Empire / reconstructing small artifacts / bug ?

[Nedman43]

Hello
I really enjoy Stellaris and like playing it, but i think there is a bug here. I enabled an advanced building by reconstructing little artifacts. When it was enabled the message told me that i could build and improve a building which is as mighty at these from the fallen empires. I will use the "Class 3 singularity" as example but i had this problem in other games with other buildings. My problem is that i cant improve these buldings. Do any other person have that problem or had it in the past? Is it a problem with my game? Stellaris runs good so far and i have also checked the local data.
Im excited to hear your answers

[alangriffith]

I could initially improve my Class 3 singularity but later I could upgrade it to a Class 4. Not sure if it was unlocked by a technology (possibly Dark Matter Drawing?) population level or what. They're weren't any new patches over the period between building it and upgrading it.

Also to be clear you can only build one (well, one per that minor artifact result). After you build it, it will annoyingly still appear on your building list but greyed out forever.