It's all clear about variance.
The weird thing is incremented "lastpayment" entry in the list without real payment occured. I believe updated "lastpayment" (from ./dash-cli masternodelist full, I observe it from 3 of mine vps) means that consensus decided some mn must be paid - and there're no ways to avoid that since the enforcement is active. Correct me if I'm wrong.
It's not about bugs in the monitoring scripts. Looks like dashninja.pl calculates "Last Paid=1d8h37m20s" based on "masternodelist full" output and dashwhale shows "Lastpay=6 days ago" based on the real payment transactions in the blockchain.
Anyway I'll inform about next payment.