I doubt it is MAC or IP address as otherwise it would get upset when I change my laptop from wifi to rj45 cable, VPN to LAN, LAN in different buildings. Which I do a lot and all will result in MAC and/or IP address changing.
If I look at Licence History in QMC it shows my AD domain/user, machine name and some hex & decimal numbers which make up my machine's motherboard UUID which you can display from the dos prompt with :
wmic csproduct get name,identifyingnumber,uuid
License leasing doesn't use the IP address, but it does take the MAC address of your network adapter into account. For a simple reason: at any point in time, you can only lease your license to a maximum of two MAC-addresses.
An active lease that changes MAC-address should be ok, as it will not request another lease, only check whether the license hasn't been revoked.
The only reason for loosing a lease that I can come up with at the moment has something to do with QV Desktop having problems recognising/validating your Windows user account or its inability to contact a Domain Controller.