final cut pro freezes during 'optimize video'

Optimizing footage creates extremely large files. How much free space is on the drive that is the target for the imported media? You need 15-20% free space, especially if it's the internal boot drive.

In order to offer more suggestions, a lot more information is needed. To begin with, what are the specs of the footage are you importing? Where is it importing from? Where is it importing to? Which version of MacOS? Which version of FCP? Might also be good to post the results of an Etrecheck report.

Seems unlikely that it would be corrupt preferences on both machines, but have you tried resetting FCP prefs? It's a quick and easy thing to try. Hold option and command when launching FCP then choose Delete Preferences. It will open the default Untitled library. Open the library you were working on, set your prefs the way you like them (uncheck background render, uncheck Create Optimized and Proxy media on import, for example).

As Tom asks, do you really need to create Optimized media? Most often it's unnecessary unless you have specific playback issues.

John Deer wrote:

If it freezes on two machines at the same point it seems useless to get Etercheck.

No, no, no.

Your two machines probably have a very similar software setup, and it could well be that the same piece of third party software is causing a problem in both.

As Tom said, Etrecheck is still very much relevant. And anyway, remember that none of us has access to your macs, so Etrecheck is the best way any of us has to have a clue as to what is going on.

Etrecheck is a diagnostic utility. You can download it free from the website.

Its report will give us more information, so we can look for possible causes of the problem.

Impossible to tell without some detailed information. What are the exact specs of the media? Why do you need to optimize?

EtreCheck is one way to possibly tell what's going on.

What’s the issue? How did getting a card reader resolve it? What were you using before with no card reader? The problem hasn’t been reproduce by others.