I submitted journal in the field of psychometrics about one year ago. Three weeks ago, the status was changed to "review completed". However, today it is changed into "editor assignment pending". I am not sure what this means. Can you help?
It's not certain what it means without knowing the particulars of the journal's internal handling, but a likely meaning is that the paper has been handed off from the associate editor who has been handling the reviewing to a senior editor to finalize the decision. In many journals, an associate editor provides a recommendation for the decision, but a senior editor actually makes the decision; if there are multiple senior editors, then a brief gap before one of them takes up the paper would create the observed behavior.
Bottom line: you are likely to see a decision shortly.