EDITED: pls reread

CRC check is running as long / only if you keep the driver settings window open.
There should be zero CRC errors or this indicates a transport problem.
Typically being caused by bad or too long cables.
USB2 cables may be 5m long, but I would try then with shorter cables for a test to exclude that, e.g. 2m.

I made very good experience with Lindy premium cables which are (at least for USB3) up to 3 times shielded.

But maybe the error could also result because of the USB port that you are using.
Check all USB ports and preferrably use those ports coming from chipset.
In USB3 (which is not the case for you) there can be issues with e.g. some ASMedia USB3 chipsets.
With USB2 I am not sure whether there are similar issues.
But I would preferrably use USB ports from chipset.

An alternative is to use an add-on USB3 card (maybe the proven Sonnet cards with FL1100 chipset).
They are backward compatible to USB2.
They use a driver (win10 has already a working driver included) which uses more efficient MSI (message signalled) interrupts.

You should also check your BIOS settings to remove any Energy saving.
And in Windows you should also use energy settings for "full power".
There is one setting which is hidden from Windows Workstation version (ultimate performance).

You can also try to measure DPC latency on your system.

See the many threads in this forum where I was involved.
Use extended forum search, search for ramses and the following keywords:
DPC OR Latency OR BIOS

You will find many references also background information what DPC latencies mean here and there.

Thanks again for the extra info.

I'm sorry to ask again, but I'm still not clear on that "0 CRC 5/16 err" in my diagnosis window.
Is that telling me I got an error?
I wondered if it was only the number in between the |   | that I was to focus on?

Thanks again

For the UFX+ I see here 5 counters ...

MC told already that it doesn't matter which of the counters actually increase, all should be zero.

The UFX II is a 30ch interface, the manual tells you on the 1st page that it uses USB2.
USB2 supports cable lengths up to 5m according to standards.

Whatever USB3 port you choose, the connector will connect to the USB2 compatible pins / lines of the plug and USB3 interfaces are all USB2 compatible.

But could still be a chipset/driver issue, therefore I recommended USB ports from chipset or to at least use an aditional USB PCIe card with USB3 chips, that are known to work well and have good drivers in the hope that it works also better for USB2.

Thanks Ramses for the further clarification. My UFXii diagnosis display looks a little different to that but perhaps that is due to differences between the products.

It looks like for the UFX ii diagnosis there is no reading for number two as indicated in your image above. Mine doesn't show any numbers either side of that |   |, just a zero in the middle and that is the one that is giving me trouble. When the issues begin that number starts changing. If I have understood correctly this is the USB transport so I guess thats where I need to focus.

Using a shorter cable pretty much eliminates the issue at 64 samples when leaving it recording a single channel for half an hour as a test. At 32 samples I am getting a 2 or 3 in that middle number and sometimes a complete fail (FIFO error).

The PCI USB 3 card I ordered has the FL1100 chipset, maybe it will help along with a Lindy Crono USB cable. My motherboard (MSI Z370-A PRO - I8700K CPU) has an Intel Chipset however so it should be OK in line with the USB chipset guidance on the RME website.

Thanks for the link.

So ‘5’ is one type of check and ‘16’ is another.
Therefore 5/16 in the reported data shown above in post No6 is As expected and nothing to be concerned about?

Asking because I have exactly the same numbers in my UFXii driver screen.
Thx