Not Sure if this will work for you but I had the same problem and tried everything. Every time I would use the multicam edit it would start off working and after a few seconds it would start dropping frames, lagging and being really choppy. I couldn’t even edit it was so bad. I tried the adjusting resolution, tried different codecs, searched the forums and all I found was a million people with the same problem and no answer. Tried Adobe and got the run around. Tried a previous version of Adobe. No luck. I even upgraded my graphics card and built a desktop computer with all the bells and whistles. No change. Then I started thinking about my external drive and called a friend. All of the footage I was trying to edit was on an external hard drive. It wasn’t like one of them fancy ones. Just a normal western digital. I called a friend and he said to try to copy all of the footage I wanted to edit to my MAIN hard drive of the computer in a new folder. I did that and also created a folder on the main hard drive to point all my scratch disk settings to. Then I started a new project from the new folders and made another multicam sequence with 5 video tracks and 1 audio. It played PERFECT!! No dropped frames, smooth playback with every clip. I guess the external hard drive wont let the computer pull the info out fast enough and it makes it lag and look choppy. I guess a good analogy would be that it’s like trying to drink a milkshake with a coffee straw. Once i put the footage on my main drive I’ve had no problems yet. I hope this works for you as well. I see alot of people with this issue. Please let me know if it works for you
J in Phoenix