this is the reason why the leads break when towing a horse, donkey, or mule; they freeze up after a certain period of time. This happens with foxes even if they are not on leads.
MC-144841
mobs freeze when being pulled by a lead
Resolved
Awaiting Response
0
Please check if that's still an issue for you in the latest 1.14.4 stable release or the latest 1.15 development snapshot.