Normally that has something to do with the pc of the user. Did you shut down the pc without closing the browser, use some cookie-cleaner, bluescreen or something like that?
That said the game also has an online-save feature. You can click save online and get it back with load online if the local save somehow gets deleted. You need to click load online in the first 30 minutes after loading the game though or your local save will overwrite the online save.
 "Defender Idle 2"){kind=icon}
 "Idling to Rule the Gods"){kind=icon}
 "Clicker to the Center of the Earth"){kind=icon}
 "Adventure Story"){kind=icon}
Normally that has something to do with the pc of the user. Did you shut down the pc without closing the browser, use some cookie-cleaner, bluescreen or something like that? That said the game also has an online-save feature. You can click save online and get it back with load online if the local save somehow gets deleted. You need to click load online in the first 30 minutes after loading the game though or your local save will overwrite the online save.