Leads visually disappear from hanging around an animal when it has been hooked up to a fence after a short period of time.  For the most part they still are technically there, but on one occasion it has even functionally stopped being there. I am running a Bedrock edition server through Realms where this has been happening, but it has also happened when loading a world held on my PC as well as on the Nintendo Switch. 

If there is any other bug report detailing this, I am sorry. I couldn't find anything else so I wanted to make sure you knew of it. 

The only fix I know of for this is to detach the lead from the fence post and then place it back on, but this is temporary; I have a feeling this happens due to a bug within the regards of object limitations, the first time it happened I had 4 different animals right next to each other attached to fence posts through the means of leads and the amount of animals I have attached now has only doubled, making this bug happen only slightly more frequent.