"MHF_" player heads except "MHF_Steve" and "MHF_Alex" still use old version textures(before 1.14) including
MHF_Blaze
MHF_CaveSpider
MHF_Chicken
MHF_Cow
MHF_Creeper
MHF_Enderman
MHF_Ghast
MHF_Golem
MHF_Herobrine
MHF_LavaSlime
MHF_MushroomCow
MHF_Ocelot
MHF_Pig
MHF_PigZombie
MHF_Sheep
MHF_Skeleton
MHF_Slime
MHF_Spider
MHF_Squid
MHF_Villager
MHF_WSkeleton
MHF_Zombie
MHF_Cactus
MHF_Cake
MHF_Chest
MHF_CoconutB
MHF_CoconutG
MHF_Melon
MHF_OakLog
MHF_Present1
MHF_Present2
MHF_Pumpkin
MHF_TNT
MHF_TNT2
MHF_ArrowUp
MHF_ArrowDown
MHF_ArrowLeft
MHF_ArrowRight
Besides, the bug may have probably appeared since 1.14
You can use datapacks, such as Vanilla Tweak's Mini Blocks datapack, to get around this issue in most cases. This is likely an Invalid report.