This has happened several times before. On opening my lesson for today I yet again saw that my ranking of 63% after yesterday's lesson and many before has been lowered to 62%. This is very discouraging and is innacurate.
They're not accurate in any way at any time! Because what they are measuring is not fluency in a language at all. Just how fast and frequently you tell the computer what it expects to hear. Hence you are likely to have a higher hit rate when that figure is based on a lower number of vocabulary/sentence items 'taught' - it could almost be inversely proportionate to fluency!