Zombified Piglins take fire damage

It's not just a sunlight issue, Zombified Piglins are taking damage from all fire sources, including lava and magma blocks. Sunlight is just another source of fire damage.

I noticed that, it's horrible!

it's intentional since you can spawn a zombified piglin on the overworld by hitting a pig with channeling while it's thunderstorm, only ghast, magma cube, blaze are immune to fire damage since they are basically fire

It doesn't seem to be intentional since zombified piglins (formerly zombie pigmen) are made to be immune to fire. But piglins and hoglins do adapted to the heat of the nether, but still takes damage, see MC-172087.

I also want to add that while caught on fire, if you try and attack half of your attacks dont hit and do damage. These zombified piglins must be lagging and are not supposed to get caught on fire.

zombified piglins still take fire damage in 1.16.0.58

Partially fixed: they don't take damage from the sun but still do from fire, lava and magma blocks.

Shulkers have the same issue. They also take fire damage. MCPE-33236

Totally fixed in 1.16.0.59.

This issue still occurs on MCPE for the Beta Version. Generating a Zombie Piglin with Trident Channeling and a pig results in a Zombie Piglin on fire that dies if under a tree or not exposed to rain. Zombie Piglins can, however, walk in lava without burning.