@paviro maybe 99% sure. FYI what I did yesterday as follows:

1. Format & rewrite the sd card,
2. Boot and run sudo apt-get update & upgrade & reboot,
3. Install MagicMirror2 with the bash command,
4. git MMM-PIR-Sensor in modules folder and run npm install in MMM-PIR-Sensor folder as well as useradd command,
5. Add code in config.js with

                {
                        module: 'MMM-PIR-Sensor',
                        config: {
                               sensorPIN: 4
                        }
                },

6. After rebooting, run MM with pm2 and shows “White Screen”, I checked the pm2 error log shows something like “Expected 49, got 48” as before,
7. Run npm rebuild --runtime=electron --target=1.3.4 --disturl=https://atom.io/download/atom-shell --abi=49 in the MMM-PIR-Sensor folder,
8. Run pm2 restart mm and it works.

I found there is another issue when a rebooting finished and MM runs automaticly with pm2, MMM-PIR-Sensor will not work(screen always on) until the sensor captured a motion.