I would recommend closing the DAS core then re-opening for a re-sync. Or use 'Tools > Wallet Repair' to update the files/transactions/blockchain whatever your issue may be IF that reboot does not work. (depends on your core, options, files, connection, network, peers, masternodes, etc.)

PLEASE remember to backup any important DAS core files (wallet.dat, das.conf, masternode.conf, etc.) along with your backup info (addresses, privkey, masternodeprivkey, outputs, etc.; depending if running as a wallet and/or masternode) in a text file in a SAFE, secure location (encrypted usb stick, printout in safe, etc.). That way if anything ever gets corrupted or lost, you have everything you need to rebuild your wallet, core options, masternode(s), etc.

Regards,

Your friendly neighborhood crypto_patriot (NOT dev)