Hello, I made these things on a project:
Create project, make it parallel, fill the tasks, complete the tasks.
Then I entered the values to make it daily recurring, and converted to single actions type.
Now it’s vanished. I cannot find it anywhere: completed, backups, text search. Nothing. Like it never existed.
First thing might be upgrading to more recent version of OF (3.8 on https://www.omnigroup.com/download/) See if issue remains. If so, might be time to contact tech support directly (Help -> Contact Omni)
Maybe you deleted it accidentially? That can happen very very fast. Sadly Omnigroup did not integrate a Trash-Bin for deleted events or a confirmation dialogue before deleting a task or a project. Hope more people can write to the support and ask for this critical adjustment in Omnifocus.