I was wondering why the Faithful resource pack needed to be downloaded every time I restarted Minecraft on my PS4 Pro. I think I know the issue.

It turns out that the resource packs are being downloaded to:

/largedownload/premium_cache/resource_packs

It appears that this is a temporary cache for when you download resources from the Store. However, the only issue is that it is imported into the wrong directory, and so is deleted when the cache is cleared. This can be confirmed by viewing the Pack Info (the green tick when choosing a resource pack).

EDIT: I'm not too sure if the cache is actually cleared or not, as the storage size of Minecraft keeps increasing every time I download the resource pack again