See plots for Max Latency each test, specifically runs 131 and 132:
http://build.wiredtiger.com:8080/job/wiredtiger-perf-long/plot/

The max reported latency in these runs has increased dramatically, up to the 5s mark from an average down near 1s.

This should have started with some commit between ba5cccea14a2afae8dc62765735be809908e0e39 and 0bad9147528b3fa7bc6d0af815e3359a3f21f2af