i had exactly the same problem ! i lost 500 xrp because of these errors !
Do you mean that you really lost 500 xrp the way that they just vanished, or kind of lost that amount of xrp by Kraken related delayed trades? Both are anyway unacceptable.
yes i had error messages(i don't remember exactly what, should have taken a screen shot) saying something like try again later... which i did, which processed multiple orders! and yes, because of that and the time delay i lost 500 ripples !