Friends not receiving invites for multiplayer

Two friends have regularly been inviting each other to worlds on mulltiplayer but since yesterday they have been unable to receive each others invites. We can see they are online, and are able to send an invite but no invites received at the other end.

No settings have been changed. We have signed in and out of XBox live. Accounts are set to accept and receive requests. Both have the same version of minecraft.