There are some of the underground amethyst diodes that do not open into caves. They only open in a hole generated in front of it. I think it's a generation error.
MC-208895
Generation error
Resolved
Duplicate
0
Hey there!
This looks to be a duplicate of MC-205854. Just to further inform you, this issue was later marked as "Works As Intended", so this is completely normal behavior that you are experiencing.