problem description

When scrolling inside the spreadsheet while the browser is getting and rendering data , zss show a blank content and it makes the function look broken to users.

steps to reproduce

1. load the attached file with default preload row / column size
2. scrolling down (or right)

current result

ZSS shows a blank content for several seconds

expected result

ZSS can show a busy message like "rendering" when it shows a blank content.

workaround

• set preloadRowSize, preloadColumnSize with a larger value
  The workaround will make the scrolling sluggish. When users reach the end of the “cached” area, users will also have to wait longer for the white screen to go away and will think that the system is broken.