Without reproduction it is impossible to resolve it. However, RDMA_CM_EVENT_ROUTE_ERROR usually mean that there is no route to specific host. You can verify it by using simple 'ping' command. Try to analyze routing table on your host (maybe it has duplicate entries), if you are using dual port card, check if disconnect one port makes the issue go away.
rdma_resolve _route depends on OS kernel routing and if it doesn't work, RDMA route resolution will fail.
Verify that you are using the latest version of Mellanox OFED stack.
Be sure to use latest firmware version
Be sure you are using subnet manager that comes with Mellanox OFED stack
Check the output of ibv_devinfo command and be sure that 'guid' of the node are not '0' (zero's).
Check 'dmesg'/syslog files,maybe you'll see an additional info that will help.
As additional diagnostic, check with 'ib_read_lat' application for example and using' '-R' flag. if it works and your application doesn't , check the application code.