This week the wallet got stuck (out of sync) for 3 or 4 times. Restarting it solves the issue.
Are you running more than one DRK wallet on your computer (using different -datadir)?
I was running multiple wallets, and also synced them simultaneously. This led to my ip getting banned by nodes (they probably thought I was trying to dos) so I had trouble syncing.
I used to get this problem when syncing 10+ wallets at the same time. I used to use a batch file that loaded all my wallets at the same time.
To get round the problem, I configured the batch file to pause for 90 seconds after starting each wallet. It might take a good few minutes to start them all but I find that giving each one a headstart with synching prevents them getting stuck.
I'm running just one darkcoin wallet with the default install.
If devs are interested I can share the debug.log.