Custom items created through add-ons have component tags which change its appearance: "minecraft:hand_equipped" and"minecraft:foil" are good examples of this. While these function perfectly in a singleplayer world, and on a host's client, this isn't true for any new players which join. Any player which enters the world (after downloading the appropriate resource packs) sees the item rendered improperly. Items with said tags use the default rendering; without the re-oriented texture or the enchantment glint.

This is likely because behavior packs are server-side, while resource packs are client side. Because these attributes are defined in the behavior pack, they therefore are only used on the server and its host, and aren't distributed to the connecting clients. 

While I was using a Windows 10 PC, I was also playing with an iPhone. I used the same add-on on both, and tested connecting both ways, and it held true; it seems to be a problem not associated with any specific version on Minecraft, but rather the way behavior packs are handled with the server.

The two screen captures were taken on the Windows 10 PC;

Steve is the PC player, the custom character is from my iPhone.

In one image, (with the sand) Steve is hosting the game, and the items are properly rendered, on his end. On my iPhone, they are not rendered correctly.

In the other, (with the trees) Steve has joined the game, and the items have lost their visual attributes, on his end. On my iPhone, (the host), they are rendered correctly.

Please note that this does not effect gameplay, but rather is a visual issue.

Yes, I did clear cached data beforehand, to see if a previous version of the pack in the cache was somehow overriding it. I have only observed this issue in the latest version, but only because I hadn't been in a situation where this is applicable.

Have a good day, and a Happy New Year!