This happened after the latest update where the hero used to pass through mobs and attack what's targetted, unlike now, it will attack/target the closest one and somewhat ignore manual targetting.
This might not be important but I really like to target ranged ones first 😗
Yeah we did have modified the locking system in the latest updates, but this is indeed a bug because we don't want to influence you to lock an enemy manually. We will fix that bug in the following updates, thanks for your report.
Thank you for your consideration. Appreciated 😊