Zoho Sheets App doesn't work anymore - iOS 10.0.2 issue?

I'm using the "Zoho Sheet" app on my iphone 6 (iOS 10.0.2) in parallel to the browser on the PC. Up to Tuesday or Monday it was working fine, I was able add data to the sheets when I was on the road. But since Tuesday (2016/10/11) the application hangs when I try to display a sheet, on the upper screen the rotating circle is visible with text "Verarbeitung ..." (German for "processing"). I tried to kill and restart the app, doesn't help. I tried to reinstall, doesn't help.

On my iPad 3 (iOS 9.3.5) it still works.

It seems to depend on file size or content. I have sheets which still work, but the most important one (according to Murphys Law) does not.