Cubik Studio

How come ?
I know that Minecraft only supports the rotation in the same plane.
But I accidentally turned UTB more than one!

If you check "PE entity" or "Optifine" in Model settings > Minecraft, elements rotations are unlocked and you can't export to Minecraft JSON with such elements.

This whole rotation lock/unlock will be improved in future updates.

To fix your issue, Reset element rotation by clicking on the anchor button in Recover panel.