The last time I used it Online save required a manual import of the data. Go to the More>Options menu and scroll down about 1/2 way and there should be some info about the online backup, including the option to "Import Online Saved Data". It is beta so your results may vary but it should, in theory, allow you to pick up your game in another browser if you choose not to perform the fix listed below.
It is probably way out of scope but I would love a simplistic language of some type for coding the AI. Even something visual with basic if-then abilities. This reminds me a lot of some old AI code games I played years ago.
I have had the glitch as well when playing while my PC was creating an ISO image. When a lag spike would hit there would be a momentary pause and then my entire horde would be gone. No evidence of impact and very consistent, every lag spike = dead horde.
This game is really quite horrific when you think about it. We are blaming these children for the sins of their fathers, condemning them to death with no jury or any real evidence of their crimes. And out choice for death is a slow an painful method after we apparently coaxed them into a false sense of security in obviously hazardous conditions. 5 stars!