Why would the review system status go from "awaiting recommendation" back to "awaiting referee assignment"?
What could also have happened is that the initially assigned reviewer first accepted to review the paper, only to then forget to do so. At the end of the time that he/she had for the review, the journal editor might have sent a reminder only to then receive an apologetic note stating that the reviewer does not have the time to do so - then the editor would have to find a different reviewer. All these things have happened. If you want to make sure what is going on, you can always send a friendly note to the journal editor and ask about it. They are human after all.