Avatars set on ENS names that are very long don't have their backgrounds generated by the metadata service.
For example, this ENS name has an avatar set which can be confirmed via the metadata service and manager app: "ocanadaourhomeandnativelandtruepatriotloveinallofuscommandwithglowingheartsweseetheerisethetruenorthstrongandfreefromfarandwideocanadawestandonguardfortheegodkeepourlandgloriousandfreeocanadawestandonguardfortheeocanadawestandonguardforthee.eth"
[manager app] [metadata service]
However, the background isn't generated for it:

The link in the metadata service background image field returns: "There is no avatar set under given address"
[metadata service background image]
Avatars set on ENS names that are very long don't have their backgrounds generated by the metadata service.
For example, this ENS name has an avatar set which can be confirmed via the metadata service and manager app: "ocanadaourhomeandnativelandtruepatriotloveinallofuscommandwithglowingheartsweseetheerisethetruenorthstrongandfreefromfarandwideocanadawestandonguardfortheegodkeepourlandgloriousandfreeocanadawestandonguardfortheeocanadawestandonguardforthee.eth"
[manager app] [metadata service]
However, the background isn't generated for it:

The link in the metadata service background image field returns: "There is no avatar set under given address"
[metadata service background image]