Overdraw on First Load

I beleive this is overdraw right? I've read previous posts about this but haven't been able to find a way to prevent it. It's suddenly begin happening on every first connect to my server, and is immediately fixed by simply reloading the shaders (Iris - Complementary). I'd like to solve this so my players don't need to hit reload every time they start playing now. I either need to find what's causing it, or find a way to automatically reload the shaders upon joining. Anyone know any common settings in Complementary that could cause this, or a way to prevent it? DH cave culling doesn't seem to help, thanks!