MacOS – All my reminders are gone

I use MacOs 10.14.5 and all my reminder lists, except one, have disappeared.

MacOS Catalina Beta is installed on a separate test partition and all my reminders are present. But they do not appear on my main partition.

Is there a way to recover them?

I do not have any iOs device. And when I go to iCloud via the web, it just indicates that reminders are coming soon. I have tried to restore reminders via iCloud on the web, but after the restore they are still not present on 10.14.5.

Ideas? Thank you!

(Note: this question has also been posted here)