Keep in mind that the timestamps Ignition gets from an OPC UA server, or generates in its own drivers, is almost always the timestamp of the poll, when the change was detected by OPC, not the actual timestamp when the signal changed in the real device. This means the ordering will be pseudo-random for signals that changed close in time, less than the poll interval.
If you really need sequence of events, you must timestamp precisely in the PLC and then buffer transfer to Ignition.