Online rating on Etterna decrease after having a score lower than the top play

I was playing Maid of Fire (1.1x) last night and have a lower score than my top play. The next morning I turn on my pc to play Etterna as usual i noticed my online rating decreased from 19.11 to 18.95. Is this a score calculation bug or something ? Just started playing Etterna for 3 weeks, don’t know much about this game

(sorry for my bad english)