Like in Java Edition, as confirmed with MC-69801, when using the Health Boost effect (not to be confused with Absorption) the added hearts are empty. However, it's impossible to replenish them.

What I expected to happen:
Using any method of healing, such as being in Peaceful mode, or using effects, the additional hearts should replenish, like in Education Edition.

What actually happened:
The added health did not replenish with any sort of healing. I am unsure if this is only a visual bug.

Steps to reproduce:
Make sure cheats are on.

1. Set gamemode to survival to view health (such as `/gamemode s`)
2. Give the effect, in this example Health Boost V for 60 seconds: `/effect @s health_boost 60 4`
3. Attempt to heal, such as: `/effect @s instant_health 60`

Note that the screenshot is actually from Education Edition, which does not contain the bug.