Minecraft has been crashing for me a lot lately but I just started noticing this issue two days ago.  My game crashed, I logged back in and everything seemed normal.  I was boating home with my dog in another boat behind me and the lead broke.  I turned around and he was gone.  After a while I went home and switched to creative mode to teleport to him and it said there was no entity found by his name.  Yesterday I found another dog, and when I logged in the game crashed within 3 minutes.  Right before it crashed I made my dog sit.  I logged back in and he was gone.  I tried teleporting him again, and it said there was no entity.  Both the dogs I have lost were both tamed and given name tags, and it has only been happening to the dogs I most recently tamed.  If this bug could be fixed I would be so happy, I dont wanna lose another dog