ROS v6.0
02:01:59 async,ppp,info ppp-IT: reseting link… - could not acquire serial port
02:01:59 async,ppp,info ppp-IT: disconnected
ROS v 5.25 - excellent work 
It seems that v6 has lost support for several usb devices that were working in v5. The only thing you can do is send supout and the model number of your device to support@mikrotik.com and hope they add support back into v6