I suggest watching https://www.openfhe.org/portfolio-item/homomorphic-encryption-for-palisade-users/ to understand how CKKS encodes real numbers (or reading the introductory sections of Approximate Homomorphic Encryption with Reduced Approximation Error). At a high level, real numbers are scaled up by the scaling factor (2^{50}) and then rounded to integers (I am skipping the FFT-based packing for simplicity). So the sum (for the first modulus size of 60 bits) should not exceed roughly 2^{10} rather than 2^{50} (see my response where I pointed to to this). Otherwise you will have an overflow. You can either decrease the input size (losing in precision) or add an extra level (to get extra 50 bits) to resolve this.
There are multiple topics in this forum discussing/explaining the overflow behavior, e.g., EvalAdd does not add in some cases - #7 by ypolyakov, Can it come to overflow by multiplication, CKKS Bootstrapping gives incorrect results on scale != 60? - #6 by ypolyakov.