So upgrading to CoreBoot 4.7 (see the forum post as well) is raising this issue, further search reveals that the issue is with the latest libusb-1.0-0 package v1.0.22 which is part of the recent update of PureOS. A patch has been added to the kernel on 27th April, so I guess it will eventually find its way into the PureOS core udpate…hopefully sometimes soon.
[EDIT] I raised an issue in the pureOS tracker.