Kea 1.9.4, a development version, has a significant known issue listed there that will be fixed in Kea 1.9.5. There is a bug in the upgrade script that is supposed to update the database schema. The upshot is, we do not recommend updating to Kea 1.9.4, and instead, if you are running the development branch, you should wait for Kea 1.9.5.
ISC funds the development of this software with paid support subscriptions. Contact us at https://www.isc.org/contact/ for more information.