The hub has its own supply. First thing I tried when having trouble was plugging the dongles directly into the Mac chassis USB. Same behavior when it happened. I am starting to suspect my PSU now, unfortunately...Is the hub bus-powered or does it have its own mains supply? Dongles tend to play up on bus-powered hubs because they have anti-tamper electronics that trigger on the brownouts you can get if they are drawing power from the host computer over the USB bus.
In the mean time, I do have another response from VSL saying that actually in my case, since only some licenses were affected, they would have been able to take care of it for only 50-100 Euros.