Check your audio device and if it uses a driver be sure to use the latest version of it. Also, depending on how large the projects are it may be related to system resources, that the system is overloaded which affects timing. Try transforming some things to audio if that's the case.
You can also try refreshing Studio One's application settings to see if that helps..
1. Go to Help>Open Settings folder.
2. Copy the contents of the folder over to a folder on your desktop.
3. Close S1 and delete the contents of the settings folder with the exception of the user.license file as well as the "Extensions" folder.
4. Open S1 and go to Studio One>Options (Preferences on a Mac) to reconfigure your settings.
5. Test to see if the problem is resolved. If it is not, please feel free to copy your settings files back over from the backup that you created in step 2.
*If you are missing presets or Sound Sets after doing this, simply double-click one of your Sound Sets under Documents>Studio One>Sound Sets.