I assume you used symmetry to place them?
This has been known for a long time to be possible:
And even reported here on the forums before:
also using the 2 times symmetry does not cause Mutiple nuclei.
i think you were doing it wrong then
Honestly, I think this is not a bug… rather a feature.
it’s a bug
it’s like bugs in bethesda games though
If it was a feature then the nucleus would need to be placeable multiple times. This is clearly a bug if you can only make multiple nuclei appear by using symmetry, which is a feature not all players even realize exists, to place them all at once.