The refining infusion enchantment seems to have gone back to the original thaumcraft numbers with a 75% chance at level 4 to convert ore to a single cluster and has no chance to generate extra.

This change started with the 1.31.0 version.

Yeah, seems like its somehow related to mixins and updates of some mods. Thanks for report, I will try to investigate.

This may have started happening in 1.30.0. I recall not getting clusters sometime before the update to 1.31.0