This happens when you put your phone on vibrate not when you turn on sleep mode. Is this happening because you have your phone go on vibrate when sleep is enabled?
You could try turning off notifications for the "mode" settings. Go into settings, then modes (not sure if this is the right word since my phone is in a different language, but it's where you find the different modes you can set your phone to), then click the three dots on the right and choose settings. Then you should be able to find "notifications" and by clicking that you get to a screen where you can choose to turn of sounds and vibrations on the notifications.
Hello there! @Ennah said it best with their troubleshooting suggestions. I had to double check the method myself but it worked swimmingly! Once you utilize the steps you will be good to go.
If you have any additional questions afterwards, don't hesitate to reach out to us again here the community and the moderators are more than happy to offer additional assistance!
