Thank you very much for your support and advice.
I put an URL image manually and the logo is display, but I am surprised to see that the site title is not displayed anymore. It is replaced by the logo.
Deactivating plugins doesn’t change anything.
Same problem with yours others plugin Planco, Phantom.
On Phantom it is not possible to delete the existing logo, still remain the preview logo. This possibility to delete the image parameter on logo exists on Tycoo and Planco theme.
Why using the same server, same plugins it doesn’t work on Phantom ?
Thank you for your help.