When breaking the Gobber Lucky Block, it appears to "despawn" just before breaking, rather than actually breaking.

It drops the appropriate loot but doesn't make a breaking sound or emit breaking particles.

This is true when using vanilla tools or modded tools. Video contains an example of both, and a stats comparison (identical item stats)

Using version 2.6.61, only config changes are the # of vein spawns per chunk (lowered)

This is a side effect of how I have the block drops. I "remove" the block and spawn in drops rather than allowing the game to break. This is cosmetic to me, but I will revisit in the future to see if it is something I can refine.

That's Fabric only right? Never happened on my prior Forge pack

This is no working like regular blocks in Gobber Fabric 1.20.6+