There is a memory leak in Domino 9.0.1 FP4 that is specific to TLS.. It is fixed in an Interim Fix (IF2), and the same fix is supposed to be in Fix Pack 5 to be released in November. The memory leak will cause the nHTTP process to crash and take the rest of the Domino server with it. I currently have this issue with three Traveler servers running the same exact versions. Also, Traveler 9.0.1.8 is now out, so you may want to consider that.