Usually, the “Editor Assigned” status indicates initial editorial screening before assigning reviewers. In the case of manuscripts that require revisions, it is not uncommon for journals to get them checked by reviewers once again. In your case, it is possible that the revised manuscript was taken up by an editor/associate editor (Editor Assigned) who was to run a basic check on your paper again and find the relevant (or the same) reviewer(s) to check the revisions (Under Review). It may have changed back to Editor Assigned either for a final editorial evaluation and decision or because of reviewer unavailability. If you have been waiting to hear from the journal for a really long time, consider sending a submission status inquiry to the journal.
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