If those are revenges, then there is nothing to inform and no bug at all.
Those players use a strategy called cup dropping, it’s used to fill hero chests fast.
I would never use it but I’ll use myself as an example on how to use it:
My best team has 3500TP and currently I have 2200 cups (platinum). It’s 11pm and I’m going bed. Before that I set up a really weak defense team, lets say five 1* heroes. Next day I wake up and see that 20 players attacked me (they destroyed me because they have teams much stronger that can easily crush my five 1* heroes), so I lost 600 cups that night. I’m now 1600 cups (gold).
I don’t want to revenge those players, insted I roll for other opponents. I find players around 1600 (±300 which means 1300 - 1900) with probably 2800TP. Since I have 3500TP I can crush them all pretty easy and climb again, while filling my hero chest in a blink and open when I’m back in platinum with 1800+ cups. Even I can spend gems to speed up the chest to open it again.
Lets say in the process I defeated a 1400 cup team, and after all the battles I ended up again with 2200 cups. Next time that poor victim connects and wants to revenge me, that player will see a 2200 cups opponent, way ahead than his/her current 1400 cups
Your partner is that victim.