Having trouble in fleet

You can basically lock someone around for about 6 to 7 minutes even though the battle only last 5.  I forget the exact mechanics, but it relies on starting the battle, going into airplane mode, the force killing the app. You can't log back in after this for a few minutes (I don't remember if that is the exact method, but it is similar to that, been a while since i had to do it since I'm not in a highly competitive shard anymore).  

The game is designed so that you don't have to be connected to the internet for the entire battle, only starting the battle and at the end to report the results.  But if you have spotty internet, they have designed some flexibility in that end report.  And while it is waiting for the end report from your device, the game will still consider you to be "in battle" and will not allow you to finish.  So the concept is that if you turn off internet and force close, you device can't report on the end of the battle, so the game will wait a long as possible, past the 5 minute timer for you to report back.  If you never report back, the game finally decides the battle was a time out and releases the lock (this is the grace period which is 1 to 2 minutes).  

So how is this working if your opponent is also beating you?  Well, not sure if that is possible, so might be multiple people involved as others have suggested.  But you can abuse the above idea (assuming you can confirm the exact mechanics of it) to try to lock your opponent out sooner than 7:30 before payout.

The eaiser method - have you tried reaching out to them to find out  what's going on?  Maybe there is an arena shard chat you can join?  Or alternative, change your payout to soemthing less competitive?