As you can guess from the error messages, webCoRE is checking whether the timezone has been set up and being told no.
It would be interesting to know what the location looks like when viewed in the legacy environment via the IDE, and also in the new enviroment (e.g. via the CLI or other access to the REST API). Specifically is the timezone actually set in the legacy environment?
It could be one of those unintended consequences things like Sunrise/Sunset where removing Hello Home (routines) also removed the Weather Station child app. That was fixed by making it a child app of Smart Lighting and adding it whenever a Sunrise/Sunset automation was created in that. Actually that would be worth a try in this case. Something somewhere has to create the timezone.