Have not had this problem with earlier versions, but have not been trying to process 4K video either. Laptop is Intel I7, 12 GB memory and over 100 GB SSD memory. Can't move the pointer at times and no response. Trying to exit, it just sits there until the "report problem to Microsoft" screen appears. Forcing me to do a manual save anytime I make any change. Clues from anyone as I really like the features.
You don't say what device recorded your video.
Open your original video in the free download MediaInfo. In MediaInfo, set View to Text and then copy the text of that report and paste it to this forum. Once we know the complete specs of your video we'll better be able to advise.
Meantime, do a simple test. Open a new project and add, say, 10 photos to the timeline. Does the program play smoothly without crashing? This is a big indicator that the challenge is with your video footage.
Without more information I'm guessing. But, would you look at the settings for default audio hardware? If not set to 'none', would you try that?
I'm looking forward to hear the results of your tests with a photo-only project.
Otherwise, that's a nice camcorder and most of its settings should produce easily editable video. You're editing 4K, so your hardware specs are definitely a factor. You say you've got an i7, which should offer plenty of power, but you don't say which i7 processor you have.
Also, how much of that 100 gig hard drive are used up? SSDs are great performers, but 100 gig doesn't leave much wiggle room for the program to process large video files. I start to panic if my computer gets down to under 50 gigs of free space. A 4K project might well choke on a full drive.
Also, look under the program's Edit menu. What is listed on the General page under Project Settings? With 4K in particular, matching project settings to video specs can be a big determiner of your performance.