Element existence validation is a preventive measure to help you avoid errors during execution. This is important because cleaning up a failed execution can be a cumbersome task.
So ideally there is NO need to uncheck this to proceed. If you have to, then there must be some mistake either in workflow design or bug command Reservation/Verification
I can help you understand it and find the root cause if you can provide your workflow here ( exported in .dar file format)
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