I had a problem, and it turned out ACYMailing was out of date. I wasn't getting update notifications from Joomla.
I looked at Update Sites in the Joomla admin, didn't see anything for ACYMailing, and I rebuilt it. Still nothing.
Please try to download the latest version from your account on acymailing.com and install it manually. It should resolve your issue.
In case it does not resolve your issue, please raise a support ticket (https://www.acymailing.com/support/) so we can have a closer look at it.