Last tested: May 6, 2020
Is it a pivoted query? If so, it could be a case of “When the clock strikes midnight the visualizations come alive with a mind of their own.”
The series editor is based around the pivot value of the series, so any visualization settings you have set on the pivoted series (colors, vis type, y-axis settings, etc.) will revert to default settings if those pivot values change. That is, when the pivot values returned by the query change based on new data, different filters, etc., the saved vis settings on the original pivot values will not be carried over to the new pivot values.
Although this behaviour can be confusing, it is intended functionality, so you can go ahead and add your vote for this feature request if you are thrown off by this behaviour. The workaround is to turn the pivoted series into table calcs using pivot_index() to make sure the series names never change.