I can confirm this issue is still present in 1.16.3. So far the best way i've come across to fix it in-game is to summon mobs with their max health attribute in the command; like /summon minecraft:sheep ~ ~ ~ {Attributes:[{Base:8.0f,Name:"generic.max_health"}]} then if you get its data the max health will show in the data command output
Marshell Kenway
I can confirm this issue is still present in 1.16.3. So far the best way i've come across to fix it in-game is to summon mobs with their max health attribute in the command; like /summon minecraft:sheep ~ ~ ~ {Attributes:[{Base:8.0f,Name:"generic.max_health"}]} then if you get its data the max health will show in the data command output