mail disappearing from inbox

For the last couple hours, messages that have just come into my zoho mail account are disappearing from view. In some cases, I have opened and read them, but when I return they are gone; in others, my inbox indicates that there is new mail, but I cannot see any new messages. They do not come up in any folders or under any labels, or when I view all messages, but they do come up when I open my inbox in outlook. (I usually use zoho online on my Mac laptop.) They do come up - as "undisclosed" recipients - on my android phone (accessing zoho online through my web browser), but I cannot open them. This has never happened before. Thank you for any ideas!