When a Zombie is lit on fire, it should normally show the fire. But, Zombies do not display the fire. However, the Zombie does still take damage. This includes all types of Zombies(not including Pigmen, they don't burn), and a few other mobs, to name one, Pandas.
I have provided a video of a Zombie not catching fire in the sunlight.
Thank you for your report!
However, this issue is a Duplicate of MC-142394.
If you have additional information, please add it to that report.
Please search before reporting, as it's likely that one exists already.
Quick Links:
📓 Issue Guidelines – 💬 Community Support – 📧 Customer Support – 📖 Game Wiki