Syncing Issues - Hashrate?
Of course it isn't synced if you haven't mined blocks in a while. The assumption with networks similar to Bitcoin (and thus Dash) is that mining is constant so if a node sees that its most recent block is old, it will assume that it is not synced.

The RPC calls will check to see if you are synced and then only serve data to mining software if it is. You can just disable this check in the source code so that you can mine again.