These Commands for summoning fox’s are outputting the incorrect mob variant in regular worlds and Super-flat worlds. They are summoning the red fox variant and not the snowy fox Variant of the the entity so using the summon in_snow command works for the rabbit works but not for the fox since the snow fox you would expect to work with the command being from a cold biome.
/summon fox ~~~~~ minecraft:spawn_wild_snowy
/summon fox ~~~~~ spawn_cold
/summon fox ~~~~~ in_snow
/summon fox ~~~~~ minecraft:entity_born
 
These Summon commands are not working 
/summon fox ~~~~~ minecraft:spawn_wild_arctic
/summon fox ~~~~~ minecraft:spawn_wild_red
/summon fox ~~~~~ minecraft:fox_snowy
/summon fox ~~~~~ minecraft:fox_red
 
/summon wolf ~~~~~ minecraft:wolf_ashen
/summon wolf ~~~~~ minecraft:wolf_black
/summon wolf ~~~~~ minecraft:wolf_chestnut
/summon wolf ~~~~~ minecraft:wolf_pale
/summon wolf ~~~~~ minecraft:wolf_rusty
/summon wolf ~~~~~ minecraft:wolf_snowy
/summon wolf ~~~~~ minecraft:wolf_spotted
/summon wolf ~~~~~ minecraft:wolf_striped
/summon wolf ~~~~~ minecraft:wolf_woods