Artist not found, don't know why

Hello everyone,

I have currently 2 artist which are unkown in plex : Carl Orff and John Williams.

I've read the help here : https://support.plex.tv/hc/en-us/articles/205661857-Changing-Artist-Album-or-Track-Names but it doesn't work.

Here is a screen of Carl Orff bug :

And parameters :

For John williams it's the same problem but I haven't any picture :

Can someone help me ? I don't understand why it don't work.

Thank you and sorry for my english (I'm a no native speaker)