Progress in grid vanishing

I have seen a couple of reports of users saying the grid clears out after viewing the comments.

https://www.theguardian.com/crosswords/quick/17123#comment-171070732

Other examples:

> I have just completed the crossword and after scrolling down to see the comments, the whole grid has disappeared

> my completed grid disappears when I move down to the comments , and back up to see what the heck they are talking about (memory of a fish) - and the ‘reveal all’ button does not bring them up, despite repeated pressing.

> I've frequently had the letters disappear when following links on my iphone - on using the 'back' button to return to the crossword, the letters have disappeared. Tapping the grid does make it fill itself in though