Bug Material change on prefab not correctly updating

Hi,

I have a very strange bug in my project, I use version 2021.3.21f1 / URP

I have a prefab that is instanciated in the level, it had a black mat to it.

https://imgur.com/a/UYx4RoD

I decided to change this mat to a grey one :

https://imgur.com/a/wooutN6

Now, each time I first open the map, the prefab is instanciated with its old black material. In my game, if you loose, you can restart a new play and it re opens the level. Only when I loose and restart that this time the prefab is instanciated with its correct new grey material.

Any idea what would cause this ?

Thanks