I had the same problem and there was no written help on where to look for this photo. This needs expanding from Adobe's perspective. Calling the help desk was not successful. I finally fou nd it as I was working in a filmstrip of lagged photos. It wasn't u til I went back to Library mode an removed the filter did I atually fin d my merged photo, alon witht eh other 3 duplicates i had created to understand this process.
Lightroom Classic offers so many ways to do a search for photos. You can search by file name, or file type, or if the file name contains Pano, or by capture date or by keyword or other metadata. Surely one of those would have found the photo.
Lightroom Classic offers many ways to sort the photos, including by Capture Time and by Edit Time and File Type and File Name.
Surely one of these would find the photo of interest.