Tilemap and Prefab generates errors

Hi guys, in order to speed up my levels building I tried to take my "basic" tilemap gameobject and make it a prefab but it seems creates errors :

- refresh case sensitivity failure
Also a warning :
- the GUID for "my prefab blabla" is already in use by "same prefab blabla here". Assigning a new guid.

It doesnt prevent the game from running but it seems to mess up my palettes who then appears empty :/

Any idea about what is going on and how to prefab tilemaps properly ?

Thank you all