Version Information

Forge version: 14.23.5.2836
Botania version: r1.10-361
Other mods: Baubles & AutoRegLib

Steps to reproduce:

1. Create a default superflat world
2. Assemble a Gaia ritual site, as per the book's instructions. Placed directly on or slightly in the ground.
3. Attempt to insert the catalyst.

What I expected to happen:
The Gaia Guardian spawns.

What happened instead:
"As hard as you try, the Beacon will not accept your sacrafice. You believe the ritual grounds might be improper. It might be a good idea to check for obstructions in the nearby area or large gaps in the floor.

the red dots tell you the missing blocks you need to fill in.

move beacon 1 layer lower is easiest fix though, (possibly pylons too.)

That will not do it. I tried that before. Question is, is anyone else also encountering this issue?
Edit: I tried that again, and it worked. I am quite confident I did do so before, so I am confused as to why I couldn't before.