Sometimes notes can be split from the main stream. Don't worry, it's fixable so that you can everything together in one place.
To do this, you can use the Merge Notes button in the upper right hand corner.
Go to the note that you want to merge into (Note A) and click on More Actions --> Merge Notes, and select the note that you want to add (Note B) from the list.
Afterward, you will see one continuous stream with all those notes.