AMD has since confirmed to us that this is its current guidance on the matter. The advice comes as just that, advice, and it doesn't appear that these steps are guaranteed to resolve the issue for all users. However, it appears the company is getting closer to the root of the matter. Here's the short version of the advice, with emphasis added to the most relevant bits:
"Based on user feedback we have received; the suggestions below could improve or resolve general USB device stuttering issues.
1.) Verify that your motherboard is updated to the latest BIOS version and configured using optimized/factory default settings. Check your motherboard manufacturer’s website for BIOS update and download instructions.
2.) Check if your Windows 10 is on the latest build and fully up to date. For information on updating Windows 10, please refer to Microsoft article: Update Windows 10
3.) Ensure that the Ryzen chipset driver from AMD is installed and up to date. Latest Ryzen chipset driver version is 126.96.36.1991 .
If you continue to experience USB connectivity problems after following the suggestions above, you may consider using either of the following workaround:
1.) Set PCIe mode from Gen4/Auto to Gen 3 in the BIOS
2.) Disable Global C-State in the BIOS.
These settings are found in the BIOS. Please refer to the motherboard user manual if more information is needed."