This issue has been solved, please update to latest version.
Our deepest apologies! Grid Diary 3.1.0 will crash if you enabled iCloud sync. This is a critical bug so we had pulled it from App Store until this is resolved.
What should I do then?
Well, stay tuned for the next update. We've request an expedited review to Apple.
A temporary solution to avoid crash at start
Please don't delete or reinstall Grid Diary, you can use local storage instead as a temporary solution! You can reset the app to use local storage by deleting a file, which is shown in the following snapshot. (You need a copy of iExplorer on the Mac or iFunbox on the Windows to do that.)
Then you can recover your data by access advanced setting for database.
Once again, our sincerest apologies!