We're running UI-testing of JMC 6 on Ubuntu 14.04 (64-bit) with JDK 9 b101 and experience a lot of silent crashes were the exit code is 134 (and sometimes 1).

Sometimes we get the following console output:
[xcb] Unknown request in queue while dequeuing
[xcb] Most likely this is a multi-threaded client and XInitThreads has not been called
[xcb] Aborting, sorry about that.
java: ../../src/xcb_io.c:179: dequeue_pending_request: Assertion `!xcb_xlib_unknown_req_in_deq' failed.
Java Result: 134

This happens when we invoke Robot.createScreenCapture() but, notably, it only happens occasionally.