you said that This can be fixed via a resource pack
but which resource pack and where cen i get it?

I am having the same problem, figure it out yet?

apparently, depending on whatever resource packs that's enabled in your game, you would have to remove each resource pack 1 by 1 and refresh them to see which pack is causing the items to float. in my case i use Alacrity and after i disabled it, the items on my character rendered properly. the bigger question is, how to fix this problem once you have figured out which resource pack causes it.

Check the other issues about rendering issues

Position and size of items can get adjusted with a resource pack, check out the readme.