Hi STEPHAN,
Generally availability of J2EE systems data will comes from Technical monitoring.So make sure that Technical monitoring working fine for J2EE systems.
Mandatory checks for Interactive reports:
1)Managed system setup of J2EE should be green.
2)Enable TechMon for J2EE systems
3)Go to SOLMAN_WORKCENTER-->technical monitoring-->system monitoring-->Then select you J2EE system-->click on you system
4)In the resulted screen you will find all metric information of J2EE system.Here make sure availability of J2EE should green if J2EE running fine.This is the source of availability of J2EE in "Interactive reports"
Thanks,
Prakashreddy