Final Cut Pro X 10.3.4 (!) on High Sierra - crashing

Start by deleting preferences. They can become corrupted and cause all sorts of problems. Hold down command and option while starting and click Delete Preferences. Then open your library and try.

Yes I followed that advise too after disconnecting the monitor it works. I have the LG utlrafine 27" 5K monitor.

Seems like I have to disconnect the monitor, open final cut pro, then connect the external monitor back on again.

*****...

I had a similar experience, maybe this will help -

After updating to High Sierra I couldn't get any library to open in FCPX at all. After a bit of trouble-shooting I discovered that it was all to do with my A/V Output (I have a Matrox I/O & a Blackmagic Intensity Shuttle). After disconnecting all of my external A/V sources, FCPX again runs like a charm.

No client monitor or monitor speakers at the moment but I'm guessing that this is just a case of Matrox/Blackmagic updating their drivers and will be fixed soon.

Same issue, except not using an LG external display. I am using two Dell 4K monitors with USB-C to HDMI adapters. Disconnect the monitors, start Final Cut works perfect. I can even reconnect the monitors and it keeps working. Very irritating, but it works at least. :-/

Everything that I explained happened on the following Mac with the following specs: MacBookPro13,3 with Intel Core i7, 16GB 2133 MHz LPDDR3 and Radeon Pro 460 with 4GB VRAM.

I think External Display issues have been common for a while. I noticed that the LG Ultrafine 5K Display had issues on macOS 10.12 while using a program called OBS and at times when trying to changed the audio settings. Final Cut X did not have issues with 10.12 Sierra, but now fails with 12.13 High Sierra while using any external displays. I have two Asus 1080p displays at my workplace and the LG Ultrafine 5K Display at home.

The workaround for now is to open the MacBook Pro's lid and wait for Final Cut X to open and load the library properly. Then the lid can be closed afterwards.

I suppose I can use the workaround for now, but you know Apple's motto: Apple devices "Just work". Considering I paid over 4k for my MacBook Pro, I would like to think these type of issues should not be part of the experience a customer should worry about for extended periods of time. Let's hope Apple is able to resolve the issues and keep the faith customers have put on their products going.

This thread says you need to launch FCPX with the laptop open:

Final Cut X (10.3.4) crashing on external display

https://discussions.apple.com/thread/8087074

Does that work?

I disconnected my monitor and it now works. Kinda weird not sure why? Any ideas?

Trash your preferences again. Reboot.

You're going to have to uninstall using the plugins' installers and reinstall. Where are these plugins from? Any particular brands? Hopefully not Pixel Films.

Make sure you trash prefs after crash or you’ll just reproduce the behavior.

Curious why you’re making a compound immediately after importing. What are you needing to do that for?

I had the same problem and had to get rid of High Sierra and reinstalled Sierra, all HONKYDORY now.

I am not going to buy the new FINAL CUT PRO that works with High Sierra.

I gave up on High Sierra with Final Cut Pro X and switched back to Sierra, when and if the update to come works, then I will use High Sierra.

Recover back to Sierra, I did that and have Final Cup Pro X working great, unless you want to buy the program again for $300, to use High Sierra. I also found High Sierra to run a little slower, my 3 Macs have 16 M of Ram !.

I tried closing FCPX, exiting, restarting, exiting/closing and then restarting FCPX and THAT SEEMED to resolve the problem. If it doesn't, I'll let you-all know.

Normally user assembly their material in a project.

Trashing prefs is fine because 95% of the times if the application crashes the preference files will be corrupted because they were saved correctly during shutdown.

You may also have a conflict with other software, or the external drive isn’t correctly formatted or needs updated drivers.

But whatever.