Final Cut crashes while rendering feature film.

You could spend a lot of time messing about trying to find out what is wrong but you might have multiple problems due to the Migration Assistant carrying over stuff from the old computer. It really is a bad idea in general.

As Tom said a while back, you are best doing a clean install of the system. This would involve wiping the drive though which you might now want to do. In that case, you could do a clean install on an external SSD. You can start afresh from that and copy relevant and important files over. Presumably you have another backup of the library and the clips etc on a separate drive, even the older Mac if you still have that. You should be able to render out from there at the correct resolution assuming you have all the necessary plugins to install as well as FCP.

Once you have all your files sorted and are comfortable installing the system, you could then reinstall on the new internal drive.

1. What version of FCP is it?
2. Have you deleted your FCP environment settings? (Start FCP while holding down option+⌘)
3. Settings →Playback →Uncheck back rendering
4. Select library →File →Delete generated library file →Delete rendering file →All
5. What is the capacity and remaining capacity of the export location?

To reinforce what has been said: migrating EVERYTHING is often a cause of problems. Migrating the user accounts is fine, though

And yes, if you have cleanmymac then it’s no surprise that problems arise.

Please run Etrecheck and post its full report here.

Use the “additional text” button and paste the report into the text box.

As others have stated, my guess is the random crashing is likely due to software migrated from your old machine. Without an etrecheck report it's tough to say. Would it be possible to take the new and old machines back to the Apple Store and have them wipe the new machine, do a clean OS install and then only migrate the User info from the old Mac? You then download fresh copies of Applications from the AppStore and 3rd parties.

Whenever the application crashes you should trash the settings. Hold ⌥ ⌘ as you double click the library you want to open to launch the application. A dialog appears asking you if you want to Delete Preferences. If you don't do this while double-clicking your library, the application will open a default Untitled  library.  

Try to export the file. If it fails again we’re need to see what’s happening with your system. Please post an EtreCheck report https://etrecheck.com giving the application Full Disk Access in Privacy & Security System Settings. Copy the report and use the Add Text button to paste the result into reply box. 

Unfortunately that’s not the best option for users of pro apps. You should consider doing a clean install of the system migrating only the users and reinstalling the applications without antivirus apps, cleaner apps, and Chrome.

Whilst there can be problems with new computers, it is very rare and most trouble is down to user-error.

How long is the film, what is its resolution, what are the specs of the original media and how big is the Library?

Where is the media stored?

Give as much information about your project as possible. The more you can tell us about what you are doing and exactly what happens, the more chance we will have of spotting what may be amiss.

Some people believe that problems can be caused by having CleanMyMac or Chrome installed.

Did you by any chance use the Migration Assistant to set up your new Mac? If so this might be at the root of your issues as it can cause all sorts of problems.

That’s the backup. Find the original library, same name without the date/time.

When LocaAlicia tells you to delete the "environment" settings, on your computer they may be called the "Preferences".

Follow her instructions and in the window that opens select Delete Preferences or Delete Settings.

Did you open a backup data library? Does it have a date/time listed at the end of the name?

I found the library and I lost some recent edits.

Find a library? Are you sure you have a backup library open?

The library must first be opened in the location where it was saved. I must be doing something wrong because I don't lose my edits when I delete the preferences.