We have been seeing an increase of BF due to change streams tests timing out.
 
This was not expected and in general can be a sign of something that is not working correctly. However, it could also be that, due to random test scheduling, we are hitting some bad condition in which we are simply doing too much. 
Despite this, we should aim at shipping code with TSAN enabled. 

We still run TSAN for replica set builds. Only sharding builds will be impacted.