TROUBLESHOOT
VOCALOID3 Editor
It may be improved if "Maximum Number of Undo" is edited.
Please check [Settings[ → [Preferences] → [Others] → [Undo Limitation], and if this is set to "Unlimited", please change it to appropriate number like "50 times".
If you are unable to find a solution in the Troubleshooting section, please use the Inquiry Form to submit an inquiry.