Upfront won't load - Errors in console

Upfront won't load - Errors on console
Ticket Description: Upfront isn't loading up in my site. Nor the theme editor nor the Upfront builder. I have no plugins active other than Upfront. There's an error which appears in the Browser Console:
https://monosnap.com/file/kv4WrW33kK4QluftnX5Dt68ZtHEcFS