I found a better fix for me: use NBT Editor to set "Leashed" to 0 .
I got five crashs for my five leashed animals and everytime "unleashed" one of them with help of the crash report to find it. So after starting minecraft five more times it now works. but still some Mobs dont load. for the time being i will try using boats instead of leashes.
Same crash but with donkey.
Maybe it has something to do with entitys dissappearing and reappearing. Before the crash trader, traderllama, villagers and said donkey did randomly disappear (when going away and back they did not load) even standing right next to where they should be and trying to teleport them to me did not find them. Reloading the world did fix it most times but doesnt fix the crash.
I got the items in creative but changed to survival for enchanting. Screenshots above.
On one world it crashed multiple times but I thought it didnt crash when I approched. Cant say for sure.
Confirm 19w09a
and special case for leads: a leashed animal will be leashed to the original fence (if possible)