My printer is the BQ Prusa I3 Hephestos. I am using the fine profile. I had an old firmware so I updated it with their latest. Same thing. I never had this issue with older Cura versions eg. 15.04. I have also tried two different laptops, one running Windows 7, the other running Windows 10. This has happened on different print files also. My next try will be to save the G-code and print it using 15.04.