I think there could be an issue with the network or blockchain or something, but it's an American holiday today so I'm sure Dan won't be available to look into it today.
I have found the below procedure to work for me.
Anyone having an issue should get onto the Troubleshooting thread in XCurrency's Slack. Seems to be sorted.
I wouldn't say the root cause of the stalled sync has been sorted.
We've simply noted that if you delete the blockchain and database and begin to resync from scratch (oftentimes having to close the app and restart it when the sync stalls numerous times along the way) that eventually the wallet will sync up and remain synced for some time thereafter.
I have had this problem periodically with all POS coins so I'm not sure what to make of it.
But seeing as how I'm not the only one, it may be worth further investigating the issue.
Maybe it's an issue with how things are commonly set up on users' computers. Maybe it's an issue with POS itself.
Regardless of the cause, the result is annoying.