The latest Windows Defender updates sometimes register Mozaik as a threat and removes it from your computer. See below on how to restore:
1) In your Windows notifications (or when the pop-up occurs) click on one of the Threats found notifications:
If the Pop-up/Notification has been cleared you can click your start button and go to Windows Settings
From there click Update & Security
Then Windows Security and Virus & threat protection:
2) From here click on Protection history:
3) Here you'll see a list of the Threats removed/blocked:
4) Select them and if they show that is related to Mozaik in anyway choose Restore or Allow depending on the option:
Afterwards, Mozaik should be back up and running with the executable restored to your C:\Mozaik folder, but you may need to recreate a shortcut for your desktop (Right click the icon and choose Send to Desktop (create shortcut):