I have genuinely no clue as to why this is the case. If you spread sculk onto a tree, you can clearly see that the sculk veins spread onto the leaves but don't even touch the logs. I've had a look, and logs don't have any tags that would stop sculk veins from spreading on them that leaves don't, and yet sculk veins simply do not want to spread up logs.

same test without leaves:

also has a low height limit, does not spread over the entire length of the tree

also has a low height limit, does not spread over the entire length of the tree

That's because veins (how I implemented them) are meant to only generate on the adjacent blocks to a new Sculk block, they won't go down an entire tree because that's simply too complicated to add in and would likely be a performance hazard.

I have genuinely no clue as to why this is the case. If you spread sculk onto a tree, you can clearly see that the sculk veins spread onto the leaves but don't even touch the logs. I've had a look, and logs don't have any tags that would stop sculk veins from spreading on them that leaves don't, and yet sculk veins simply do not want to spread up logs.

That's because Sculk growths aren't spherical, they're circular. They'll try to find a nearby surface that can be replaced, they don't intentionally search for walls. Btw, are you able to test this with logs on the floor? If this doesn't happen in that case, it's just because of how I implemented them.
Keep in mind that I didn't want veins ruining performance when searching for a block to go to, so I limited their search radius to 3 blocks up and down. I can always change it to 5 if needed. The veins went onto the leaves because that's where the initial block was chosen, not the placement for the four additional veins.

The veins went onto the leaves because that's where the initial block was chosen, not the placement for the four additional veins.

ah, okay, that's understandable

Btw, are you able to test this with logs on the floor? If this doesn't happen in that case, it's just because of how I implemented them.

will do once i'm home

Keep in mind that I didn't want veins ruining performance when searching for a block to go to, so I limited their search radius to 3 blocks up and down. I can always change it to 5 if needed

again, understandable. i was under the impression that this was just an issue with logs.

again, understandable. i was under the impression that this was just an issue with logs.

there's a small chance that something got screwed up with a random tag, it could be the case

again, understandable. i was under the impression that this was just an issue with logs.

there's a small chance that something got screwed up with a random tag, it could be the case

i've checked through every tag and every bit of sculk growing code at least four times each, nothing refers to logs as being unable to spread sculk veins. testing this behaviour with any other block should be pretty conclusive