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For your initial conditions, drdt has an imaginary part. Differential equation solvers in SageMath generally only work with real values, so desolve_odeint using SciPy doesn't give an answer as expected. The solver desolve_system_rk4 uses Maxima and shouldn't really be returning an answer: that looks like a Maxima bug.

If you set r(0)=1 to keep the system real, you get the same answer from both solvers.