Cyborg's Scan doesn't always work

Cyborg's Scan skill sometimes doesn't steal beneficial effects, even when you KNOW that it worked due to Cyborg getting healed (the skill heals 15% hp for every beneficial effect stolen). I've noticed that this seems to happen most against Gunner Corrupt Rescuers (whose titan shield is buggy as all hell when it comes to stealing it ─ often the shield won't work on the toon who stole it and the GCR will immediately replace it even when it's not the beginning of her team's turn yet). This has led to some lamesauce moments in PVP where I nearly lose due to Scan working (by healing hp), but not working (by not actually giving Cyborg the positive effects).