Confusion regarding manuscript status in IOP's article tracking system and ScholarOne Manuscript System
“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.