mongos needs to store OpTimes instead of Timestamps, in order to include the correct term when running GLE commands on shards.
In pv1, mongos will receive a valid term in the optime it gets as part of $gleStats. This term can be used in the wOpTime field of a subsequent GLE command, and everything should work as long as the shard remains in pv1.
In pv0, or from a 3.0 shard, mongos will receive no term in $gleStats. It will store a sentinel invalid term for such timestamps, and use just a timestamp for wOpTime in a subsequent GLE command.