Whenever the player or mounted entity takes damage or heals, the heart icons do not always blink. When they do occasionally blink, it is not as apparent as it normally would be and only occurs when the entity takes damage.
If you look closely at the heart icons in the attached video, you can see that they sometimes briefly blink, but only when taking damage.
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We're tracking this issue in MCPE-33658, so this ticket is being resolved and linked as a duplicate.
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