Re-install the Datylon for Illustrator in case of a major Adobe Illustrator upgrade.
In case you install an Adobe Illustrator CC major upgrade, you should re-install the Datylon for Illustrator 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 26.1.1 to 26.2.0 is a major upgrade.
More info on installing Datylon for Illustrator in the following article.