An intentional stress test was done around block 19450 and further. The network was flooded with hundreds of transactions per block, consolidating inputs mined in thousands transactions earlier. It seems that the daemon accepts some malformed inputs and even worse accepts such block broadcasted from another node if it has some matching inputs in mempool.
The only workaround to this until it is further investigated is to resync and mine new branch if your height is increasing and is above 19488, and do daily backups of blockchain database until a reasonable fix is released.