Hi @Kirill_Bunin Thank you for reaching out & I'm so sorry to hear about all of the lost work 
Since you're not seeing anything helpful in the history, I would recommend stepping back in the page saves history using the _historyOffset url param (instead of the history tab) as described here One of my screens seems to be lost - #10 by Tess
Is it possible that there was more than one tab/window with the app open in edit mode? If so, this could have possibly caused page saves to overwrite each other and clear your work. We are working on a beta feature called multiplayer that will allow multiple editors to use an app at the same time