Google Colab revision history were lost

The revisions I made in a google Colab virtual notebook all disappeared from past three days (I can still find older revision history before these missing 3 days). I can still see in history that I edited the file yesterday, but very strange no revision versions from any of past three days. Any way I can rescue code that I wrote in past three days? To be clearer, the current version I can see was from 3 days ago, any modification I made in past 3 days were gone, and no history can be found, except the editing history says I edited the file. Again，in short, my recently changed code all lost, anyway I can rescue...