My mules seem to lose hearts in their heartbar as soon as they become Adults

I crossbred 3 different horses and donkeys. Each time the Foal becomes a Mule and I mount it. I Notice its missing Hearts from their Health Hearts Bar. This all in Version 1.16.221 I couldnt put it up there cause it would respond with "Version with id '1.16.221' does not exist.
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