Soul-Scar Mage is bugged
I cast lava dart onto arcbound worker as a control a soul scar mage. When it dies it has no counters on it but it did trigger its modular ability still
This is not a bug.
Cancelling +1/+1 with -1/-1 counters, and the creature going to the graveyard are checked in the same state based actions.
When it dies it looks at the last previous known state of the creature, which is a 0/0 with X +1/+1 counter and X -1/-1 counters. It thus sees the counters and triggers.
For this issue, please submit at: https://mtgo-support.wizards.com/hc/en-us/requests/new and select 'Reimbursement Request / Report An Issue'.