somehow the ore veins will float in the air
Maybe add a compulsory solid block replacing rule will fix this?
Does it relates to generating event orders?

Those are BEAUTIFUL ore veins... What's weird is I believe in order to end up like that, they have to have generated AFTER cave gen, rather than before. That's not something you control, it's just the way MC WorldGen works... Truly a strange thing.

The ore veins are generated before the caves. They're not features but a special step in world generation, most likely for performance reasons, and this mod expands on that. The reason vanilla veins don't have floating blocks is that iron and copper ores are in #overworld_carver_replaceables. You can add the custom vein blocks to that tag to make it so that the caves destroy those blocks.