Email notifications to Observer accounts include a link to "Click here to view the comment".
Previously, this took the parent to the actual submission. Now it takes them to the assignment itself and does not show the completed work or grading.

I have spoken with a helpful Canvas Support colleague today who has told me this is currently intended behaviour. One of two things now needs to happen:
The link is restored so that it points to the Submission, not the Assignment, again
The link is altered so it does not read "Click here to view the comment"

I would strongly recommend option #1, that this behaviour is restored back to previous functionality.
I'm aware that parents can click Grades and then view all grades for that course but this is extra actions to achieve a goal that shouldn't need it and is currently actively misleading