Duplicate entities

I tried reproducing this by using the server jar for 19w02a. After trying this for a few minuts and didn't happen. How did you 'disconnect'? You got kicked because of an error or you logged out yourself? Does this happen all the time or rarely?

I disconnect with the button, but it's happen an other time when I leave the chunk and when I return to thie chunk. It happens all the time, or almost all the time

In order to reproduce it, you have to relog outside of any permanently loaded chunks (outside of spawn chunks for instance), in any dimension. Only if, it will duplicate the mobs around you upon reloading. They can sometimes be invisible, or be inside each others, but the logs will complain about entities with same uuid.
This issue relates to how entities are being tracked upon loading chunks, especially duped entities only appear on the global entity list MC-141484.
This issue is the same as MC-138871, MC-138919, and causes the spawning "keeping entities with same uuid." in the logs MC-95649.
A workaround for this issue is to /forceload the chunks where you reload or go to/from the Nether or the End.

Wouldn't that mean it's a duplicate of  MC-138871 and/or MC-138919 as well?

I think so.