NotImplementedError: Cannot convert a symbolic Tensor (2nd_target:0) to a numpy array
For me, the issue occurred when upgrading from numpy 1.19 to 1.20 and using ray‘s RLlib, which uses tensorflow 2.2 internally. Simply downgrading with pip install numpy==1.19.5 solved the problem; the error did not occur anymore. Update (comment by @codeananda): You can also update to a newer TensorFlow (2.6+) version now that resolves the problem … Read more