PM2 Stops app at unexpected times with SIGINT "process killed" and the reason is not clear - pm2

Question

The app stops and I can't figure out why.
I start the command like this CMD ["pm2-runtime", "main.bundle.js", "--cron", "0 */16 * * *"] (should mean to restar the app every 16 hours)
Then I see the app starting:
15:35:02
2020-01-09T15:35:02: PM2 log: Launching in no daemon mode
15:35:03
2020-01-09T15:35:03: PM2 log: App [main.bundle:0] starting in -fork mode-
15:35:03
2020-01-09T15:35:03: PM2 log: App [main.bundle:0] online
And after half an hour I see that it's stopping the app.
16:05:32
2020-01-09T16:05:32: PM2 log: Stopping app:main.bundle id:0
16:05:32
2020-01-09T16:05:32: PM2 log: App [main.bundle:0] exited with code [0] via signal [SIGINT]
16:05:32
2020-01-09T16:05:32: PM2 log: pid=30 msg=process killed
16:05:32
2020-01-09T16:05:32: PM2 log: PM2 successfully stopped
I see no errors in my app and I can't understnad why it stops.
Another end log:
06:11:52
2020-01-11T06:11:52: PM2 log: Stopping app:main.bundle id:0
06:11:52
2020-01-11T06:11:52: PM2 log: App [main.bundle:0] exited with code [0] via signal [SIGINT]
06:11:52
2020-01-11T06:11:52: PM2 log: pid=16 msg=process killed
06:11:52
2020-01-11T06:11:52: PM2 log: PM2 successfully stopped