People report that the app seems to be hung forever in "Checking Encryption keys".
Please leave the decryption for multiple minutes until it completes. It will eventually.
"Forever" is a quite flexible term here. Omni has chosen quite strong encryption which is both time and memory hard. This means that on phones which dont make use of hardware accelerated crypto, this will lead to multiple minutes for the initial calculation of the keys. If your phone has less than 3GB of RAM or an older processor this might even take longer.
Unfortunately, this cant be helped.
Android is quite bad in common crypto support, which means that different hardware vendors support different crypto algorithms in which case FocusGTD has to fall back to software based algorithms (which in turn cause long decryption times).
Note that this only affects the very first sync (and every time you wipe your data). All subsequent syncs should be faster since certain bits are cached.