We're not really sure what's causing the visual issue, but what's happening is our WX-78 player is using the Victorian head skin along with it's respective outfit, and when he mounted a fully tamed, Ornery Beefalo with a Glossamer Saddle, the Beefalo became invisible. The WX then proceeded to switch to a different head skin, the Unfinished, while keeping the Diving Gear on, and the Beefalo still became invisible. Finally, I believe the WX switched to the Magmatic set and the Beefalo was visible. It was only when the WX was mounting the Beefalo that the Beefalo became invisible.
I did capture a clip of it from my stream, if you're not quite sure what I mean. Note that there is foul language so if you need to mute the audio, I understand.
Be WX, equipped with the Diving Suit (I believe?), and get on an Ornery, fully tamed Beefalo with a Glossamer Saddle.