On MTGO, Forgotten Ancient make u put each counter on one at a time. i had Pir, imaginative rascal on the field with forgotten ancient and literally doubled all counters put onto Pir. as i looked it should only add 1 extra as you should determine how many counters to move at once. It should work like hardened scales.
For this issue, please submit at: https://mtgo-support.wizards.com/hc/en-us/requests/new and select 'General Questions'.