A lock free read using linearizable read concern that runs concurrently with replication step up causes an fassert here: https://github.com/mongodb/mongo/blob/06a96bad7c0c5413b785776b5d0e51d436ecc958/src/mongo/db/db_raii.cpp#L300-L303

The read source will be left unchanged as it is not modified for linearizable read concern but the flag that indicates that an update is needed it set because the node is not accepting writes yet. 

https://github.com/mongodb/mongo/blob/06a96bad7c0c5413b785776b5d0e51d436ecc958/src/mongo/db/db_raii.cpp#L257-L264