I noticed in Device Manager (under Windows 10) that there are six entries named Unknown Device under Other Devices with a warning overlay in their icons.
I right-clicked on them, clicked Properties, and in Details tab I can see for all of them, under property hardware ID, the description ptun0901.
I did a brief search on the Internet and found that the problem seems to be a missing driver for OpenVPN TAP-Windows Virtual Network Driver.
The strange thing is that I've never used OpenVPN, not consciously at least. I don't even know precisely what a VPN is, and don't know which device could need it. So the question is "Should I download the missing drivers (from the OpenVPN site), or should I simply click Uninstall Device? Is the second one a safe solution?"