For Smart Date fields with recurrence, you can either set the recurrence to "ends after" a certain number of instances, or "ends on" a specific date.
The site I'm working on has content with a mix of these two options. It appears the content editors just choose whichever one they prefer.
In the views of this content, the content which "ends on" a specific date does not sort together with content set to "end after" a certain number of instances, but is lumped at the beginning or end.
Create content with recurring Smart Date field, some of which is set to "ends after" and some of which is set to "ends on". Create a view sorted by the date field.
Note I'm not sure if this is due to something I'm doing wrong; I've found Smart Date and Views to be a bit of a pain. Feel free to reassign this to a support request if it's not a genuine bug.
Active
3.7
Smart Date Recur