tier1304
Hi,
The detailed statistics are only available in the paid Acymailing versions.
You can try to run a database integrity check in Acymailing->Configuration->Security. If that doesn't resolve your issue and you have a valid Essential or Enterprise subscription you can raise a support ticket for this here: https://www.acymailing.com/support/.
Please note that you can't rely on the open stats if your goal is to be sure if someone opend a mail. Opens are only counted if a user clicks on a link (links with personal information in it are exclkuded) or downloads images. Most mail clients do not show images by default. So if someone reads your mail without downloading the images or clicking on a link, you have no way of knowing that the mail was opend.