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So are you reporting that:
a) you lost an attack, but due to a bug you still have your win-streak?
b) you haven’t lost a battle in a while, but a random attack-loss (without any actual consequences, beyond maybe losing you a few pvp points) appeared in your log?
No idea what’s causing it, but I’ve seen it around for quite a while now, happened more than once (though for me it was always the b) option). The “this pvp battle has already ended” is a lot more annoying and damaging, since it can actually give you a loss you don’t deserve (thus, breaking the streak).
I actually won an attack, but the stats show a loss. There was no error messages during fight. I had a similar bug few days ago - my defend team lost Tacet team in his stream, but my stats show a win.