For a new server; practice arena goes x-server at the end of the first month. And at the end of 2nd month; a server gets its' season feature activated; ranked arena goes x-server, and maximum rank reached gets reset; and prizes are distributed in accordance. After that your rank will be reset at the end of each month. It has always been like this, and will always be such. If it is your practice arena that went x-server, there is nothing out of order. However, if it is ranked arena then there is something wrong.