Isn't there supposed to be a shower of essence upon defeating the dragon the first time? The only things that dropped were exp, a yellow heart (Tinkers) and a shader bag (immersive engineering).

No idea what happened, made a new world, tried killing the dragon several ways, dropped essence every time.

Must have been a one time thing, but still super annoying.

Now I am even more confused. I logged back into my regular world to test, in case it was a world-specific bug, and I found exactly two stacks of Dragon Essence in my inventory. I definitely didn't have that before, but I'm fairly sure I didn't cheat it in. I had logged out from the end, so I suppose it's possible that it was just invisible until now or something...but I swear I didn't have that essence before now. How much is the dragon supposed to drop? Exactly two stacks seems awfully convenient.

There's no exact number, it depends on how well you played and the difficulty level. 2 stacks is too little, the items fly off in all directions.

I fought the dragon on Peaceful this time, to avoid the Endermen. Would that affect the amount?

Yea, but 2 stacks isn't enough anyways.

It's entirely possible it simply wouldn't all fit in my inventory. I'm going to try fighting the dragon again later in this same world...

Hmm. Something may be messing with the drops, idk.

Killing the dragon the second time for that world, on Easy this time, netted me exactly 1.5 stacks of dragon essence...

Try without any other mods, /heeadmin kill-bosses to quickly kill the dragon.

So this IS a bug, then. Now to figure out what mod causes it...

Read the /r/feedthebeast post, so I assume it's safe to close this since the conflict affects multiple mods and is not in HEE side.