Does “before” mean a few months ago or does ‘before” mean last week? 
Back in January SmartThings stopped running all custom SmartApps that ran in the free groovy cloud, including several popular ones that were used for notifications like “Notify me when.”
See the community FAQ for specifics:
Why Did My Integration/SmartApp Stop Working in January 2023?
So that’s why people are asking you exactly what you had set up to create those notifications in the first place. If it was one of those custom apps, then you’re going to have to re-create the notifications using the new architecture.
But if this is a change in the last week or so, that would be something else.