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...
