I've been messing around with item displays for my Blockbench plugin that exports animations to Minecraft, and it appears as though I've run into an in-game interpolation issue.

I've included a video of what the animation is expected to look like (recorded in Blockbench), what it looks like in Minecraft, and a comparison of a couple of the matrices that display incorrect interpolation.

How to reproduce

• Summon an item_display with any item model (It doesn't have to be a custom model).
• Place down two command blocks and put stone buttons on top of them
• Put Command 1 into the first command block
• Put Command 2 into the second command block
• Activate the command blocks sequentially and notice the awkward bouncing interpolation. 

Command 1:

data modify entity @e[type=item_display,limit=1] {} merge value {transformation:[1f,0f,0f,0.0625f,0f,-0.4243065522280399f,0.3082767551050003f,1.540635741691493f,0f,-0.5877852522924748f,-0.8090169943749459f,0.125f,0f,0f,0f,1f],start_interpolation:0}

Command 2:

data modify entity @e[type=item_display,limit=1] {} merge value {transformation:[1f,0f,0f,0.0625f,0f,-0.457812552688941f,0.23326714669302423f,1.5093316794159124f,0f,-0.4539904997395463f,-0.891006524188368f,0.125f,0f,0f,0f,1f],start_interpolation:0}