Foxes holding items are lowered by a pixel or 2

The bug

It may not be easy to spot in survival, but easier in creative with the NoAI tag.

Simply, give the fox any item that it takes (like a sword or wheat) and you may see that it is floating by a pixel or 2.

/summon minecraft:fox ~ ~ ~ {NoAI:1,HandItems:[{id:"chicken",Count:1b}]}