FCP 10.1.4 repeatedly crashes importing FS7 footage

Not sure what's happening here:

5k iMac running Yosemite 10.1.1, FCPX 10.1.4.

I can't seem to stop FCPX from crashing while I import 4k footage from a recent three day FS7 shoot. Usually, I just select all my footage and let FCPX cook away overnight. For two days now it just crashes after trying to import a few clips.

Digital Rebellion's Maintenance Tools claims it was crashing because of an outdated Core Plugin and that I should delete FCPX and reinstall. I took this fairly literally and simply deleted the FCPX app and then re-downloaded from the App store. Additionally, I decided to reinstall Yosemite to see if that might be the issue. So far FCPX has crashed twice after all this.

I have been working XAVC-I footage successfully since November, but can't understand what the issue is. My master card transfers are on a USB3 drive as is my Library. For kicks, I tried creating a new library on my Thunderbolt RAID and trying again- still no change- FCP crashed.

The last thing I might try is dumping all my footage onto my RAID, but don't see why this would matter. Is it that it's 4k and FCP is freaking out?

Try making a new user.

I did trash preferences and also did a full reinstall of FCPX this time- using AppZap to delete everything. I also dumped all files onto my Thunderbolt drive. Between these things it was able to import the footage. Still doesn't make sense to me since I have edited and imported off a USB3 drive before.

I imagine something got messed up when I moved from 2012 iMac to my current 5k using Migrate.