Jeff’s probably right.
Could be that you have clips with the same name used multiple times. For example when media managing a project and I use clip “Super Cool Shot” I may use various segments of that clip throughout the cut – because it’s a super cool shot. FCP will add a numeric identifier at the end since it is creating multiple files and you can’t have multiple clips with the same name. “Super Cool Shot” becomes “Super Cool Shot XXX” and so on. (XXX representing numeric identifiers, not the content of my super cool shot.) 🙂
Also, you may want to check and see if your clip names are very long. FCP used to have a max character and may be truncating the name since you don’t appreciate the value of brevity. That could be part of the issue, not sure if that still applies on recent versions. Lastly, if you have any non standard characters in the clip names. Like “Frank’s Super Cool Shot” or “$h!TTy Shot?” FCP may be throwing a fit because of the unrecognized characters.
Any of that look familiar?
Good Luck.
-Alex