Possible Fixes

Yes

Modpack Version

2.3

What happened?

The altar looks wrong after being auto built, but it works.
If I follow the quest and build it by hand, the controller says missing structure.
The auto built altar:

The altar in questbook:

latest.log

No response

Developer reports

No response

The multi block does work if built exactly right, which unfortunately does include those two arcane crystal blocks being placed wrong and a strict air requirement that breaks "properly built" arcane pillars. From the image however it does look like yours should work and would need more information to figure out why it doesn't, regardless a fix is being worked on by a team member.