This is most likely due to lack of number of cells in the curved sections. EME depends on the mode matching at adjunct cells. If the waveguide shape changes fast, the mode power cannot effectively be transferred to the next cell. Please try the second device with more number of cells and make sure the power coupling is correct.
You can check the mode overlao matrix at each cell and see if the coupling is lowere. Please refer to those articles:
Understanding EME error diagnostics
Convergence testing process for EME simulations
EME Convergence Testing - An Intuitive Approach
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