Iron golem/Villagers disappear/reappear when looking above them.

When viewing iron golems/villagers, if you look directly above them they entirely disappear from view, when I look back they reappear. Though sometimes they seem to disappear altogether permanently when I recreate the issue too many times. I have uploaded video of this to youtube and included the link here: https://youtu.be/lvL5QQarjdc. I'm running the Pure BDcraft Resource pack with It's included HD UI in the video but upon checking it seems to happen in worlds without any resource packs as well.