No problems with Note 4, Note 7 (
), S7, and now S9. You must have another app that's interfering since it's happening across phones.
You say it's not prevalent enough to troubleshoot by removing app, but asked for help and expressed being upset that it's not working consistently. If it's that important, it needs to be addressed. You can try Safe Mode to see if it's impacted by a 3rd party apps. Thing is, you'll have to delete those apps systematically to find which one is the cause. There's no easy out here.
Start with the basics:
- Do you happen to notice it on certain days or schedules? Perhaps there's a software conflict at those point.
- Did you restore from a backup when you setup the S9, or did you skip that part (setup as new)? Since it's happened across phones, it's possible a glitch carried over from the S7.
- Safe Mode, as suggested above.
If all else fails, use Smart Switch PC to backup all your personal data (no apps, settings, or other misc data), then factory reset without automatic restore enabled. During setup, skip the option to restore from a backup. Test. If all ok, restore from the Smart Switch backup (again- personal data only, no apps, settings, or other misc data).
Good luck.