Playing mainly with Plarium Play on a Windows PC

I'm playing this Game since 3 months and invested a lot of time and some money to make progress. The last saturday I reached finally Gold I in the classic arena after I had some problems with Arbiter mission and the Great Hall, so I had to spend much time there. Today I started playing and as always in the arena also. But what happend: my rank is only silver II ??? How is this possible? I lost over 500 points literally over night. This sucks.