Trigger two sessions on the same card at different times using DAQ Session-based interface?

I need to generate two waveform on two different analog output channels of a NI card witch should be triggered at different times. I have created two sessions (s1 and s2) with one analog output at each, and trigger connections to receive the triggers. I have also generated the trigger signals using digital channels on a third session. The problem is when I start s1 and s2 in background and create the triggers on s3, only the session which was started first will be triggered (among s1 and s2). The digital signals are generated (checked on oscilloscope) and wired to the trigger channels of s1 and s2, but only the one which is started first would see the trigger. Just to make it more clear, if I use the same approach but put s1 and s2 on two different cards, then they both will be triggered. My understanding is that on one card only one session at a time can be running on the background ad waiting for trigger. Is this true? Is there any solution to this or any alternative ways to use the same card but having trigger based sessions on the same card?

I can provide the code if it helps.