Light curve processing and period analysis for EPIC 219297228. The light curve exhibits a complex structure from multiple spot groups and spot evolution; panel a: EVEREST lightcurve (black) and the reconstruction from the PCA (blue). Panel b: PCA-corrected lightcurve (black) with large spot features marked. Panel c: result of a Lomb-Scargle analysis with the maximum in the power spectrum indicated in red and the period determined by manual inspection of the light curve in blue. Panels d and e: light curve phase folded with the periods obtained from the Lomb-Scargle and the manual inspection, respectively. For this particular light curve, the Lomb-Scargle analysis preferentially picks out half the true period of 23.14d, despite the clearly different shapes of the recognizable spot features.