Currently, for courses divided into groups, the delayed user report allows to select:

• users from all groups
• users from a single group
• users non enrolled.

This last option IS A LOGICAL ERROR.
You can not ask for users...
"not in any group" (alias: "not enrolled") && "still not submitting" (delayed)
because guest user will ALWAYS be counted.
If a user is "not enrolled", of course he still didn't submit.

The "not in any group" item, in the "delayed user" report, IS A NONSENSE
it is needed when users...
ACTUALLY HAVE submissions EVEN IF they are not enrolled
but in this report only users WITHOUT submission are searched.