Automated triage: As designed
Thank you for reporting this issue. The soft bounce threshold only triggers when all three of its values are met together: number of bounces, number of days with bounces, and days between the oldest and newest bounce. With only the bounce count lowered to 1, the other two values still prevented the account from being marked as bounced, which matches the setup in your update.
This is an automated assessment. A member of staff may review and update it.