MuseScore 4 has suddenly started lagging, despite previously being fine.

Quite a long post, so do excuse me (also new to this forum, so hopefully this is okay. Sorry if not). Basically, I have suddenly been having problems with MuseScore lagging. No idea why, and I have tried everything so grateful for any help. I've put some points to show key details, thanks!

Key Points:
- I've had MuseScore 4 for around 2 months now, since I got a new laptop. It was working fine, no lag, nothing. In fact, it still loads in only a couple of seconds, but playback and that sometimes randomly lags.
- Sometimes it's fine, sometimes not. Sometimes it seems better if I leave it for 5 minutes.
- Task Manager shows nothing wrong. I'm not seeing all my RAM used up, or CPU, not even close. It just seems to be MuseScore lagging: even RAM intensive apps like Google are fine.
- The scores aren't complicated, and lag happens on all. I probably use around 4 instruments on average. Especially because I never had lag before with the same complexity, I'm just confused.
- I'm just using my laptop's speaker. The drivers are updated (and MS is updated too, by the way)
- I do meet the requirements. RAM is 8gb, the CPU is more than enough, and as mentioned it's not consuming a lot anyway.
- I have run virus checks (all fine).

Things I've Tried:
- Doing a Factory Reset.
- Fully uninstalling and reinstalling it.
- Closing all other apps.
- Opening (and closing) the Mixer.
- Increasing Buffer Size.

Frankly I'm just confounded haha. I'm not sure how and why the app has just suddenly and randomly started lagging, despite being fine. To my knowledge, nothing on my laptop has changed. I'm getting to the point where I'm about to reinstall MS3, but I just feel like there must be something I'm missing. I'll be eternally grateful if someone can fix this, thanks for looking! As a side note, I have checked other posts (and done what they say), so unless there's something I've missed I am hopefully right in posting here.