this isnt an issue for me, maybe you didn't play any rapid before 90 days
Problem with graph in stats

yes I agree with falcon39 as my friend has played rapid games in the pas 90 days but i have only been playing rapid since 4 weeks ago

I have played rapid for over a year. This problem does not occur on the ‘1 year’ or ‘all time’ categories though.
In the statistics section, for the 90 days time category, the graph starts from 0. I am ~1400, and this means that changes in rating are barely visible on the graph. This is not a problem in other time categories, as they start from the lowest rating in the time period.