With WordPress my favicon which is a (verified) background transparent gif is displayed with google Chrome and Opera:
- in admin pages always normally
- in front-end pages always with a black square background –
With Firefox or Edge it functions normally
The favicon declarations are identical.
I think that the problem comes from any “parameter” linked to html, js or css content of pages and context. Something with changes the behavior of the browser (default value for ?)
I don’t understand at all what can happend and I have no track to follow.