I'd designed a python software that required to start right after boot into system. I'd use sudo nano /home/pi/.config/lxsession/LXDE-pi/autostart to add in @python3 /home/pi/X/exe.py
Before I'd include serial communication into the apps, everything works fine.
But after I'd add in serial, the autostart had failed.
So, how to autostart on boot a PyQt5 based serial comn.-able apps in Raspbian Jessie?
I'd been suspecting that this weird behavior is due to serial communication that I'd added, that will be used before Pi logon.
I'd decided to reflash the image and my problem is solved.
Raspbian autostarting a PyQT5 UI that has Serial communication