In cleaning up / reorganizing a lot of tasks recently I’ve found it helpful to merge tasks.
I noticed when attempting to merge certain tasks, when I would search for a task to merge into using the EXACT task name of the target task it would not show up. Other tasks with similar names would but not the one I was targeting.
After experimenting, I realized if I deleted the due date (recurring every 12 weeks in this specific case) of the target task, and then went to search in the merge function the target task would show up.
I believe this is a bug, as I cannot think of why this would be a desired function within search.
Maybe something you can clean up in a future release?