Hi, Missymist - it's nice to see you here!
Hmm... The emails... It is possible that some invoice/emails are being affected and not others. Supporting this assumption is the fact that email notifications have suddenly changed. (I posted about the changed email in another thread.) The default email might have altered for some sellers and not for others. As to why - let us look upon the terrible face of the god called Glitch, who doeth the work of eBay (sometimes. His sacred day is Friday).