The in-game health bar lacks an animation (the white flickering effect) when regaining HP. From what I've been able to gather, the 1.4.2 Bedrock update seemed to have broken this animation. This is a rather old bug, dating back to mid-2018. I have provided footage from the earliest build that still has the animation in tact (1.2.10), and compared it to the most recent version as of submitting the bug report (1.21.2).

STEP TO REPRODUCE

The only thing needed to test the bug is to take any form of damage with at least 19 hunger points, in order to meet the requirements to regain health.

SUMMARY

I'm not sure if this bug was a deliberate design change in the way that the GUI behaves, but I still feel as if this is worth mentioning, in case it was an accident.

EDIT

I originally stated you needed 18.5 hunger points to regain health. This has been corrected to 19.