Emails still in Sending status when Campaign is in Complete status

I have sent two campaigns since the upgrade to 4.0 (currently on 4.0.14). On each campaign, only about 1/3 of the emails show as Sent when the campaign completes. All the others are still showing Sending. However, there is no way for me to finish out the queue. The “Send Queued Emails Now” button is greyed out and states that there are no emails found in queue.

I have been sending via a cron job since version 3. I can see that my cron job is firing every 5 minutes as expected.

Please advise how I can release the remaining emails that are still listed as Sending status. Additionally, do I need to make a change to my cron schedule with the updates in version 4?

Thanks,
Matt