From the CA site itself ... the Sch C is not on the list of forms that can be efiled ... I suspect it has to do with the craziness that happened earlier in the year about classifying employees vs subcontractors ...
https://www.ftb.ca.gov/tax-pros/efile/individual-efile-forms.html
In May 2019, the California Office of Tax Appeals ruled very recently that income from California-based clients is taxable as California source income.
For some discussion:
https://www.coblentzlaw.com/california-office-of-tax-appeals-gives-precedential-authority-to-bindley...
https://money.stackexchange.com/questions/95243/is-self-employed-work-performed-out-of-state-for-a-c...
