Musescore playback laggy

I have pretty much the same problem. Mine is worse, though. Also I have only 4 GB of RAM on my PC and it has an Intel i5-2700 CPU. Anyone who knows the precise parameters one needs to run the new version properly, please enlighten us :)

I have the same problem and can't get a new PC or laptop for another 7 months or more.

Three of the four computers that I have MS4 on do not meet specs. All of mine are old and I can't afford to buy a new one, either. What they have in common is an SSD rather than an HDD.
Make sure your I/O device is set to your actual sound device and not "Default".
An audio interface has been the last part of the puzzle for me. I have a Focusrite that works well. I also have a cheap one that works. Years ago I broke the headphone/mic jack on an old laptop. I bought a usb plugin device replace it. Even this device at very little cost makes MS4 usable. With the right settings, of course.
I learned some time ago that the more you lighten the work load for the motherboard, the better the computer will run. My desktop that runs MS4 without the audio interface, has a nice GPU. I think that helps. What does the GPU have to do with audio? It, rather than the onboard gpu, does the work of displaying everything. The motherboard can concentrate more on trying to get MS4 to work. So, the audio interface lightens the workload on my other computers. And MS4 is indeed a heavy audio program. But the interface takes care of the audio so that the other hardware can do their job.
That's an oversimplification, but it gives you an idea of what is possible.
20 or 30 bucks for a usb headphone replacement device seems like a win. Can I guaranty it? We know most bets are off when it comes to computers. I can't tell how many times I've tried something somebody said that it worked for them, and it didn't work for me. It takes some experimentation. On one of my computer audio settings, I had to take down to low "CD quality" before it worked.
4 GB might well be a problem. Especially for big scores. But you never know.
It is "possible" to run MS4 without a new buying a new computer.

Same here, I doubt the configuration matters. I don't have an audio interface, I use a standard Windows setup. I have a powerful PC, fairly new, superfast SSD, so on. The problem is Muse doesn't use ASIO, which makes no sense to me atm. Not only there are problems with playback, but the Muse Sounds are CPU bound and botlenecked by some strange reason. There is not much CPU nor RAM used. I have issues sometimes with crackling and lag during playback. But note input is always laggy and almost unusable with my keyboard, the only way to input notes is by writing. Even in a simple piano score, even using the default soundfont, there will be a bit of lag and some strange, limited duration notes [that may be by design]. With Muse Sounds the lag increases significantly, so playback happens half a second later or more, and so.. any score that uses these sounds will start with a lag spike.. basically. I always need to start a measure early or so, to avoid this bug. Changing Audio I/O from Default to Speakers or Headphones makes no sense and no difference. Maybe we're supposed to drive sound thru some custom audio interface..