Under certain conditions, geckolib armor that you or other entities are wearing is rendered ~100 blocks out. It's unclear if this is a geckolib or oculus issue, but here it is for official tracking. I haven't personally tested with Iris Shaders.

This bug was fixed in Geckolib4, but Geckolib3 is sunset. This is just an issue people will have to deal with if they don't want to update their MC versions