I get this too with after updating to 2019.3.13… and own project totally broken…
No ecs in own project, we downgrade to 2019.2.12, and failed to create a smaller bug project
For the record I eventually stopped getting this error. I’m now on 2020.2a though. Not sure what fixed it. May have been deleting my Library folder? Clearing the cache? Or simply updating to a newer version of either the editor or a package.