This is caused by a bug in Athoms last update. - See Rounded and flattened charts in Insights.
They reduce data points as they normally only do for older data.
I recommend to complain/bug report to Athom to make sure, they put a fix high on the agenda for the next update.
[EDIT]
Just got confirmation from Athom that the problem described in ”Rounded and flattened charts in Insights” will be fixed with the next update. - I am pretty positive, that this will resolve the problem here as wel.
