As of 1.14.20, mobs no longer burn in daylight. Can confirm Zombies without helmets, and Phantoms appear to be fine during the day.
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Cleaning up old tickets: This ticket had been set to 'Awaiting Response', but has not received a response from the reporter (~3 months+) so is being closed as Incomplete. If you feel this is still a valid issue then please comment, or create a new ticket following the Issue Guidelines which includes steps to reproduce the problem.
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Tested in Windows 10 and could not reproduce. Can you provide screenshot, video, reproduction steps, or upload the world?
Also, have you spawned a Wither? Withers lower the skylight level so that undead will not burn.