• Install ArtemisLib and AquaAcro and turn on the ArtemisLib Integration
• Use a mod such as GulliverReloaded
• Crawl in front of another player with a size scaling of 1 (normal size) or less, this happen:

• Set the size scaling of the crawling player to at least 1.2
• Crawl again, it's working:
  

So basically it seems that if the player is of a size scaling smaller than 1.2, the crawling animation render is not working properly.

Some other screens, I think the issue is coming from

GlStateManager.translate(evt.getX() / widthAttribute - evt.getX(), evt.getY() / heightAttribute - evt.getY(), evt.getZ() / widthAttribute - evt.getZ());

located in the onEntityRenderPre method in the AttachAttributesFix class