At 10.50GMT, there was a clear c/trail W -> E (GIPSO - SAM - MID); at 11.00GMT there was another trail S -> N - neither appeared at any time on map. Why? Barry Aldred
I'm not part of the ATLAS team but the system only uses data from aircraft that plot their locations on the ADS-B receivers, if they do not give their location you will not see them.
Many aircraft including military, biz jets, GA, regional's to name a few do not give position reports so will not be seen on ATLAS