FCPX 10.3.4 crashes during File>Share>Master File. I have reinstalled FCPX, trashed preferences, trashed Libraries, created new Libraries with new clips, run Disk Utility, repaired permissions, restarted the computer, etc. Nothing is working and FCPX just keeps crashing on Share. Please advise! Many thanks!
Here is the crash report if it helps:
Process: Final Cut Pro 
Path: /Applications/Final Cut Pro.app/Contents/MacOS/Final Cut Pro
Version: 10.3.4 (303235)
Build Info: ProEditor-30323005007000000~1
Code Type: X86-64 (Native)
Parent Process: ??? 
Responsible: Final Cut Pro 
User ID: 501
Date/Time: 2020-03-23 11:05:06.311 -0400
OS Version: Mac OS X 10.13.6 (17G65)
Report Version: 12
Anonymous UUID: 3CF3EC37-947D-0AEC-3D73-0BF7154EEBDA
In addition to what FCPX.guru said, make sure you have background rendering disabled. Then delete all render files, then select all clips in the timeline with CMD+A, then render them with CTRL+R.
This helps segregate the render phase vs the encode phase. If it renders OK, then export to ProRes. File>Share>Master File>Settings, Format: Video and Audio, Video Codec: Apple ProRes 422. This helps distinguish between an export problem vs a Long GOP encoding problem. The ProRes output will be very large but it's only for a test.
If that works then try exporting this way: File>Share>Master File>Settings, Format: Computer, Video Codec H.264 Faster encode, Resolution: 1920x1080.
If any of those fail, duplicate the timeline as a snapshot, open that and strip out all effects with Edit>Remove Effects. Then try to export it. If that works, it's an effect or plugin. If it fails, then delete 1/2 of the timeline, and try to export that. If that works try the other 1/2 of the timline, then 1/4, then 1/8, etc until you narrow down where the problem is.
If it exports OK with no effects, then use the similar "half splitting" method on an effect-laden timeline to narrow down what timeline range has the plugin causing the crash. IOW remove Fx from 1/2 of the timeline, then 1/4, then 1/8, etc until you find it, then examine the effect or plugin used on that range.
As a standard troubleshooting procedure, make sure you are not using any hard drive which is not formatted HFS+ (Mac OS extended journaled), Do not use ExFAT, NTFS, or any NAS drive while troubleshooting this. Since the problem seems to be 100% consistent and does not require any particular data set, use a test library with only 1 clip, located on your main system drive.
It could also be a Quicktime extension, plugin or kernel extension. You can check for MacOS kernel extensions by typing this in terminal:
kextstat | grep -v com.apple
Re Quicktime extensions, I don't have the specifics for those or how to selectively remove them. If you have access to another High Sierra machine with FCPX which is *not* crashing you could compare on each machine the contents of the folders /Library/Video and /System/Library/Video. Maybe on your problem machine some Quicktime extension was installed.
If this problem began after a certain date and if you have Time Machine backups you could restore those folders to a scratch directory and compare based on that.
If that's not possible you might have to do a totally clean install of MacOS.
Thanks again for all the help. I had recently updated the OS to 10.13.6. After trying every suggestion given me, I did a Time Machine Backup and restored my OS to 10.13.2. Restarted, opened up FCPX and no crashes when exporting! I tried to solve this for a week! I hope that this helps anyone else with my configuration. Thanks again!