Astral Sorcery version 1.10.11 on the Enigmatica 2 Expert modpack on Twitch.

It seems that the artificial 'invisible' light sources creative by the Thaumcraft Arcane Lamp blocks the ritual pedestal/structure from working. As the light source is invisible I had to fill in the block spaces by around 15 y levels to get rid of the light source.

Only other light source available for my current area was the 'Cave Illuminator' so I suspect the Arcane Lamp is at fault.

Could this light source be whitelisted to allow the rituals to work regardless?

Yes, anything within the space of the multiblock will cause it to fail to form. This is by design. #986 for more information.