The midpoint review is only possible when you have logged between 30 and 74 CPEUs (between 30 and 49 for DTRs) and you submit for midpoint prior to 12/1 of the last year of your cycle.
If you submit for final review and your CPEU total falls below 75 for RDs (or 50 for DTRs) upon review, CDR will allow you add activities /correct mistakes and resubmit the log prior to May 31 of the last year of yourcycle. Submitting early for final review is a good substitute for midpoint review.
You can also delete activities to bring your total down below 75 to return the log to a point where midpoint is possible. If you refresh the page after deleting some credits, a midpoint review button should appear in the log.
Also, please note that activities cannot be added to an approved log.