While I was working on my map, Focused Location, I found this bug. There are two areas in the map in which leads are used for decoration. These areas are far away from each other and from the spawn chunks. Every now and then, I return to the areas to check something or to continue building them, and I see that 60% of the times, the leads either break and drop as an item, become invisible (Only the strings become invisible, the entity on the fence is still there) or connect to a non existing target far away and start to rapidly shake and glitch (See pictures) (This one is fixed if you follow the leads for a while).
This issue is a remake of MC-14826, however the ticket was marked as "fixed" and redstonehelper said "If you're still experiencing any of them, please create a new ticket".
EDIT: There was another effect with this issue that I noticed before but forgot to include here. Sometimes the animals that had the leash will actually not be able to technically get leashed again. You can still right click them and you'll get the leash thing, but you can't put the leash on a fence, although I think this is a different bug because this one talks about leads breaking, not animals not being able to be leashed.