The bug

On 2020-04-21 the format of player head texture data changed significantly across all versions, breaking existing commands. It seems to include a lot of duplicate data now as seen in the attached image. Certain fields such as timestamp are missing. The impact of this change is not completely clear yet, more testing needs to be done.

Cause

The response of "GET sessionserver.mojang.com/session/minecraft/profile/<uuid>" has changed. The expected response is documented here: https://wiki.vg/Mojang_API#UUID_-.3E_Profile_.2B_Skin.2FCape

How to reproduce

1. Give yourself a player head and place it on the ground

   /give @s player_head{SkullOwner:"steve"}

2. Check the texture data of the block

   /data get block ~ ~ ~ Owner.Properties.textures[0].Value

3. Notice that the encoded JSON object is much larger than before, decoding it gives you a similar result as the attached image.