Xcode 10 unexpected duplicate task: CopyPlistFile

File -> Workspace Settings -> Change New Build System to Legacy. It worked for me .

In my case, the conflicting files were not listed in Copy Bundle Resources but only in Compile Sources section.

I went in project navigator, selected the file, and in File Inspector / Target Membership unselected and again selected the app target (untick and tick checkbox next to app target).

The files disappeared from 'Compile Sources' and appeared under 'Copy Bundle Resources' and I was able to continue with the build process.

I was getting this for a core data model .xcdatamodeld, It turned out the model file was listed under both "Compile Sources" & "Copy Bundle resources" in Build Phases. Removed it from the latter and it build in Xcode 10 finally!

Faced same problem. Resolved it using following

go to Target -> Build Phases

Check if your file is appearing in both Compile sources and Copy Bundle Resources section, if yes remove it from Compile Sources