There are two problems that have plagued Resume Designer for a long time now.
The first is a crash when trying to send mail. This happens for a very small number of users. I'd guess less than 1 in 1000 based on the number of support questions I get, but it's obviously a huge problem for the people it does affect.
And the second is that for some users, when performing the initial iCloud sync, the app simply hangs.
I haven't been able to reproduce either of these problems, which has made it impossible for me to track down what's going on.
The good news is there's an easy fix for both of these: Restart your iPhone or iPad.
I hate offering this as a solution, but unfortunately, it works.
iOS is designed so that an application should not be able to affect the system in such a way that a device restart would ever be necessary to clear up a problem, so I suspect there is a bug in iOS that is causing these problems. But until I can reproduce it here, suggesting a restart is all I can do.
If you've run into these problems, I'm sorry. I wish Apple provided a way for me to contact users who post App Store reviews that mention problems, but if you've found this post, then hopefully this will help.