Try the followinhg.
In Preferences turn off Background Rendering.
In Preferences change Time Display to Frames. Go to that frame number and replay the clip at that location with something else.
With the Range Tool, Select a short section that overlaps the replaced clip. Without rendering export as a Master File. If that works, tidy up the Timeline and export.
If it didn't work…
In the project library select the project and from the File menu, choose Delete Project Render Files>All Render Files; then go into the Event Library and with your referenced event (s) selected, delete Event Render Files>All Render Files. Close FCP and empty Trash. Reopen and do the test export described above.
Good luck.
Russ