Hey there!
I found a bug with the panda entity.
When you spawn in the panda right inside of you, it dissapears at a short time...
and then when you try to place more, they don't show.
So that's a simple bug I found.
MC-138019
Panda Entiy
Resolved
Duplicate
0
Josh Animates
(Unassigned)
Unconfirmed
Minecraft 18w43b
Retrieved
Is your render distance set to 3 or lower by any chance? If that's the case, you may be experiencing MC-137521 (entities not rendering on low render distances), which was marked as fixed for a future version.