CWios

I am seeing the same behavior in version 1.9 on Xbox One.  Playing two player split screen.  When either player opens inventory, game lags for both players.

Moving items from inventory to the quick bar, or vice versa, the game also lags.

We also noticed that if one of us is carrying a Shulker box, the issue is even worse.  Both players are wearing a full set of enchanter armor and carrying multiple enchanted items as well.  If we open a chest full of non-enchanted things, the lag does not occur.  This behavior matches the original posters notes on how to recreate the issue.

Reporting the same problem on Xbox One.  Minecraft version is v1.8.0.

As the previous commenter did, have tried multiple beacon effects, removing and replacing the beacon, removing and replacing the beacon and the block beneath it, rebuilding the entire pyramid and still no luck.

We have even tried saving the game, exiting Minecraft, reloading Minecraft, and then performing the steps above, also with no luck.

Other achievements have been unlocking fine today, as we were able to get the achievements for spawning and killing the wither a few hours before attempting The Beaconator.

EDIT:  Forgot to mention that this is happening in local play, both solo and split screen co-op.  We are not playing in Realms at all.

EDIT #2:  After repeatedly trying to get this to pop, it popped when we destroyed the whole top layer of the beacon pyramid, then replaced it, building the sides first, then the middle block, then the beacon block, and then feeding the beacon.