A bug has surfaced, a malformed transaction has been crashing minter threads on pretty much all minting nodes (but not all) for past 20h or so.
To mitigate, purge mempool.
first stop the node
rm .peercoin/mempool.dat
then start the node with -zapwallettxes
then mint.
Still researching on what went wrong, expect a minor version with a patch soon.