It sounds like you've been having notification issues with your iPhone since you were using iOS 10. Not getting your messages in a timely fashion can really be an issue and I'd like to help make sure this is working as it should. When you specify SMS messages, is it because you don't have this issue with contacts that use iMessage? If this occurs with all contacts, have you checked to see if you have DoNotDisturb enabled for these contacts?
You'll also want to make sure your Notification settings are setup correctly as well. Check out the link below to adjust this to a setting that works best for you.
Use notifications on your iPhone, iPad, and iPod touch
Let me know if you notice a change.
Regards