It seems file transfers are broken with the Windows store version, and I suppose chat history comes over using a similar transfer protocol, so that would explain the loss of chat history. I found if people send me an attachment, the icon comes up but a progress bar for download never finishes. Well, I engaged Whatsapp support and I am pretty sure I am talking with a bot, or a monkey, they are giving the most stupid suggestions possible 'it takes some time to sync' 'reboot your PC' etc.
I unfortunately upgraded the version I had on my PC (as it gave a suggestion there was a newer faster version available) and it won't synch my chats when I sign in, only group membership names.
