I have killed both the Wither and the End Dragon, but neither is being counted by the Monsters Hunted Advancement.
"minecraft:end/kill_dragon": {
"criteria":
{
"killed_dragon": "2019-10-18 10:02:50 -0400"
}
,
"done": true
},
"minecraft:nether/summon_wither": {
"criteria":
{
"summoned": "2019-11-16 19:03:35 -0500"
}
,
"done": true
},
"minecraft:adventure/kill_all_mobs": {
"criteria":
{
"minecraft:pillager": "2019-10-05 14:34:27 -0400",
"minecraft:blaze": "2019-10-08 19:17:38 -0400",
"minecraft:skeleton": "2019-10-03 01:51:07 -0400",
"minecraft:elder_guardian": "2020-07-07 14:58:55 -0400",
"minecraft:zoglin": "2020-07-12 16:53:25 -0400",
"minecraft:ravager": "2019-10-27 15:58:40 -0400",
"minecraft:ghast": "2019-10-11 21:47:08 -0400",
"minecraft:hoglin": "2020-06-19 22:32:36 -0400",
"minecraft:guardian": "2019-10-20 09:24:01 -0400",
"minecraft:vindicator": "2019-10-27 15:55:50 -0400",
"minecraft:magma_cube": "2019-11-08 23:24:25 -0500",
"minecraft:spider": "2019-10-03 01:48:32 -0400",
"minecraft:creeper": "2019-10-06 00:32:27 -0400",
"minecraft:slime": "2019-10-19 23:03:38 -0400",
"minecraft:evoker": "2019-10-27 16:11:47 -0400",
"minecraft:phantom": "2019-10-16 22:52:20 -0400",
"minecraft:zombified_piglin": "2019-10-23 19:04:17 -0400",
"minecraft:witch": "2019-10-12 22:47:15 -0400",
"minecraft:wither_skeleton": "2019-11-15 20:56:05 -0500",
"minecraft:husk": "2019-11-20 10:18:33 -0500",
"minecraft:shulker": "2019-10-19 12:10:09 -0400",
"minecraft:cave_spider": "2019-10-05 22:31:13 -0400",
"minecraft:piglin": "2020-06-15 09:02:27 -0400",
"minecraft:enderman": "2019-10-05 15:32:17 -0400",
"minecraft:silverfish": "2019-10-17 22:54:10 -0400",
"minecraft:stray": "2019-11-20 10:04:47 -0500",
"minecraft:endermite": "2020-07-12 18:10:54 -0400",
"minecraft:vex": "2020-07-07 11:02:11 -0400",
"minecraft:zombie": "2019-10-03 23:07:57 -0400",
"minecraft:drowned": "2019-10-06 16:50:29 -0400",
"minecraft:zombie_villager": "2019-10-12 21:53:05 -0400"
}
,
"done": false
},