This read-only PerfCounter64 reports the total number of out-of-sequence errors received so far; it does not exist while the test is still in the initial state. It counts test frames that arrived in the wrong order, indicating reordering on the network path, likely due to load-balancing across multiple paths or buffering. For example, a nonzero OutOfSeqErrs count on a link expected to be a single point-to-point circuit would suggest an unexpected multi-path routing condition worth investigating.