During upgrade from WiredTiger SCCC config servers to CSRS, I get a backtrace on the new CSRS second and third config servers. This happens about 4 seconds after reenabling the balancer. I am using MongoDB version 3.2.1-95-g4a3c6e6

Attached are the logs for the 3 config servers. run9007 is the first config server, run9008 the second, and run9009 the third. The balancer was restored around the time 11:19:01. The backtraces for run9008 and run9009 occur around the time 11:19:05.