In the read_pref_with_hedging_mode test, the first read that doesn't throw some error on the mongos is setting a maxTimeMS of 1000ms. Since this is the first read to this collection, the mongoS is having to perform a refresh to get the routing information. On slow machines, this refresh can sometimes take enough time that the operation hits the max time.

We should either increase the maxTimeMS of this operation or perform a read at the beginning of the test to cause the refresh to happen earlier.