Hi Esben,
I did receive an update from Lansweeper about the issues we are facing about the service tags not being detected. they redirected me to the monitorinfoview link. as per them they say LS detects serial no as per this and if it matches then these are the only details LS can provide.
'Lansweeper indeed does not scan the Dell service tag currently. We've already received similar requests from our user base to scan the Dell service tag, and as such, it was added to our customer wish list. We have tagged your ticket as a feature request to add weight to this. Features on our customer wish list get development priority based on a combination of customer demand and difficulty to implement. As such we aren't able to guarantee that this feature will be implemented or provide you with an estimated release date at this time.'