When trying to run e.g. the lpcusblib_GenericHIDDevice example code with the default USB High Speed enabled (USB_FORCED_FULLSPEED 0), device enumeration is very unstable and usually does not succeed. I also lose the debug connection (target poll failure). If I however force the device to Full Speed, everything works fine.
I have started to look at the USB clocking config in SystemSetupClocking() (in sysinit....c, where I have cut code from the KEIL template) and HAL_USBInit() (in HAL_LPC18xx.c), but I cannot really see what configuration(s) could cause the USB0 device controller to work fine in Full Speed but not in High Speed.