Entity randomly despawning

So, I'm spawning Human entity on my server by plugin, but after 3-10 minutes when someone join all entities in level just despawn..
I tried lot of different ways to spawn the npc, also tried slapper, but this still happens...
Any ideas to fix this?
I'm using latest pmmp build, but tried on oldest and don't work too

 

do you just send it to the player or actually spawn it in the level.

 

Tried to send to player and also spawned in level

 

But it's still same - It despawn after some time

 

Can it be caused by Buycraft plugin from Falkirks? I updated it to new versions, so can there be bug? I really have no idea and this is only one plugin that I have on server (and devtools)

 

Tried without buycraft, but no fixed, so I don't know

 

Buycraft is 100% not related with your case, it may caused by the plugin that clean your worlds junk or any cleaner things with a period.
Send here your plugin list may would be easier to us to analysis.

 

After some hour of testing I figured out it's caused by auto save, so I deleted pocketmine.yml and it magically worked