I had submitted a manuscript in an IOP journal a month back. In the IOP's article tracking system, the status changed from "1st reviewer agreed to report" to "Editorial Assessment" instead of "All reviewer reports received". However, in the ScholarOne Manuscript System, the status changed from "Awaiting Referee Reports" to "Awaiting Decision". What should be the interpretation of the current status of the manuscript?
“Awaiting decision” is not incompatible with “All reviewer report received” or “Editorial Assessment”. It means the editor, an associate editor or a handling editor will have a look and make a decision.
Remember that referees can only recommend a course of action: it is the journal through its editor or delegates that takes the decision to publish or not, usually based on the reports.
In particular if the review or reviews are inconclusive, the editor may decide to send to another reviewer.