I assembled the board a couple of weeks ago and had some serious problems since with the USB connection. Additionally some private things I had to take care of delayed the search for the cause of the problem.
In u-blox center the raw messages just arrived sporadically and the config could not be loaded in 'configuration view'. Interestingly with debian the chip was correctly recognized under 'lsusb', in windows however not (device not recognized) WTF?!.
After some fiddling with a serial2usb converter instead of the bluetooth module I at least could confirm the correct function of the chip! I was sure that I did not destroy it desoldering and putting it on the new PCB.
[messy bugfixing, a serial2usb converter is soldered in the serial line]
On the search of the problem I measured the voltages of the voltage converter, USB_Vdd_in and USB_vdd, all seemed fine. After that I checked the signals on the USB data line, they seemed OK.
Then I remembered a passage from the manual where it states that USB is only activated when Vdd_USB is present (3.3V), so if there is an interruption / instability of this voltage line the USB functionality is activated/deactivated sporadically....like the massages
I resoldered all capacitors and the voltage regulator for that line and this solved the problem. The chip is now recognized with full USB2 speed without any more problems.
I already build a case for the device and will upload the pictures and a documentation in a view days.