As seen in BF-32613, an unclean shutdown (caused by killing and restarting a node via a SIGKILL) can have the node start back up with a bin version that is not the same as the one before the shutdown. In case of the BF mentioned, shard2's primary had a binVersion of 8.0 at the beginning and on restart came back up with a bin version of 8.1, causing the test to fail due to FCV incompatibility. 

max.hirschhorn@mongodb.com pointed out that the binVersion changes because jsTest.options().useRandomBinVersionsWithinReplicaSet causes the value the node originally had (stored in this.nodes[n].fullOptions) to change. This issue can be fixed by remembering the original binVersion between the calls to stop and start methods in the restart method.