Middle of Navarn Steppe at NPC Milden. There is also one at Valtara Mountains, north of the actual icon "Valtarra Mountains"

A big stone crab named Kamasylvia Scrub Stoneback Crab. Attack it and smaller adds will spawn, read below!

Hit the big one, and small spawn. Dont kill big one too fast

The big one can spawn small ones 2 times, and he drops 3 at the time, one of each at 70% hp and 30% hp
Kamasylvia Rough Stoneback Crab
Kamasylvia Herb Stoneback Crab
Kamasylvia Small Stoneback Crab

Kill the small ones AND use pickaxe on them BEFORE you kill the big one, or else they might despawn. (You can gain knowledge by gathering on monsters)

Do NOT drop the health of the big one too fast at the beginning, he might not summon extra at all if you do that.

Pull Big One, knock to 75% kill all the little ones, knock to 30% kill all the little ones.... Run away and reset and repeat.

found another spot

The Manshaum's spot:
map view https://gyazo.com/2ef3d2c228e7ef5f26b1daee02f55e97
mini map view with mob https://gyazo.com/e1578d53058644d1506766eb120350d9

Navarn Steppe spot:
map view https://gyazo.com/6d1aba793b3b28bb82cfe5d0442f5fd6
mini map view with mob https://gyazo.com/aae7b574cafa42b3d50ca4fc4a8e726c

https://youtu.be/jmsV6M_kIqE
Ma petite vidéo tout est expliqué dedans

This one was hard to get all 4 S's but I managed.

I've found 3 kinds of Kamasylvia Scrub Stoneback Crab. Some is big, Some is small. The biggest one will summon the other 3 crabs. I've get the guide from this video. https://youtu.be/jmsV6M_kIqE

Respawn time is 150 seconds.

4 spots

можно заагрить большого, дождаться спавна мелких, отбежать, отагрить большого и убить мелких.
u can aggr crab, wait spawn little crabs, run away, unaggr big one, kill little crabs and repeat.
https://youtu.be/-alD1KxhfJA