When you have big assets (~500 MB), and the connection from the DACCC to the DAM Center is "regular speed" (at least a couple of minutes will pass - but I will not be surprised if it took more than 20 minutes), then having the system download the images takes up a long time. During this, the program will freeze.
Please note that this is only an issue the first time you do it - after that - switching to high-res is quick.
https://basecamp.com/2748089/projects/14380370/todos/348299419