Wait 5.17, may be will be this week.
Dev work with similar bug on our RB433UAH + ROS 5.16(90-100% CPU Load by management).
Try to disable SNMP and see what is happen ?
I have this problem with one rb750up running 5.16. Disabling snmp returns cpu to normal but I really need snmp...
Another 750up and a gl don't have this problem.