This is unfortunate, but sometimes happens.
After the arm percentage is reached the hopper starts tracking the price down again. Sometimes the price can lower drastically in a very short period of time. Imagine your arm percentage is 2% and your trailing percentage is 1%, the coin goes up to 2%, but then drops with 3% within moments. This would cause your trailing percentage to be triggered and a sell order with loss is placed.
Alternatively, sometimes a sell order is placed at the right moment, but cannot be filled. Your hopper will then cancel this order after your predetermined amount of time, and will try again as the price has gotten lower yet, and the trailing percentage is ''still'' triggered, causing your position to be sold at a loss. All you can do to counteract this is to set the trailing percentage higher so there is more ''room'' for the position to recover. This can also lead to even lower percentage profits though, if the price continues to go down. We're working on more control over this process, for example resetting your trailing percentage after a failed sell order. We have recently implemented this function, check it out! We are working on even more functions to prevent selling with a loss.
Short version: trailing stop loss cannot guarantee profit. It tries as hard as it can, but the markets can be harsh