We are looking into it. Was it on Poloniex or Bittrex?
It's Poloniex (as seen on the screenshot), as Poloniex identifies Stellar using "STR", and Bittrex uses "XLM". (Bittrex doesn't have the "STR" tricker.)
Unfortunately, Polo has been having DDOS and heavy loads lately to the point where it's hard to even trade manually.
I want to personally thank the makers of this bot. I was doing some manual margin trading last night and watching it on the bot (I love the % indicators) and a couple of times during heavy traffic, the margin would disappear (not appear in the first place), but the bot saw it and I could cancel it.