Re-install the Datylon plugin
In case you install an Adobe Illustrator CC major upgrade, you should re-install the Datylon plugin after that. Preferably the latest version which can always be downloaded here. No need to uninstall the plugin first.
An Adobe upgrade is considered as a major upgrade when de first digit behind the point is increased. e.g. from version 24.1.1 to 24.2.0 is a major upgrade.
More info on installing Datylon in the following article.