Make sure to disable the "Pause sim if focus lost" option in Prepar3D/FSX.
If the sim is paused (eg because you tab out) it will not send any updates to SPAD.neXt.
If SPAD.neXt does not receive any updates from the sim for 2 minutes it assumes it crashed and will shutdown.
Current SPAD.neXt Release: 0.9.10.0