I think what I wrote is correct, but why is it giving this error?
Don’t use quiet. Then I think you’ll see that one of the iterations did not find an optimal solution, so L_new was populated with NaN, so in the next iteration, L and therefore L_pre was NaN, resulting in CVX considering expressions having NaN in the input data to be invalid.
You can look at posts in Search results for 'sca unreliable order:latest' - CVX Forum: a community-driven support forum to see the hazards of crude SCA.