Not sure what you mean here.
You mean sub-tasks I guess?
I’d advise using Advanced Search to find this.
Note that the “Any” status refers to Incomplete and Completed but does not include Deleted
Assuming you’ve modified this recently sorting by last modified would probably help.
If you can’t find it using Advanced search I’d advise to contact support and giving them all the information/clues you have. See: How to contact our Support Team 📧 
This may take longer than you like. Please carfully read to ensure you don’t act in a way that delays handling your ticket.