  We present a detailed nonlinear dynamical investigation of the Blazhko
modulation of the Kepler RR Lyrae star V783 Cyg (KIC 5559631). We used
different techniques to produce modulation curves, including the determination
of amplitude maxima, the O-C diagram and the analytical function method. We
were able to fit the modulation curves with chaotic signals with the global
flow reconstruction method. However, when we investigated the effects of
instrumental and data processing artefacts, we found that the chaotic nature of
the modulation can not be proved because of the technical problems of data
stitching, detrending and sparse sampling. Moreover, we found that a
considerable part of the detected cycle-to-cycle variation of the modulation
may originate from these effects. According to our results, even the
four-year-long, unprecedented Kepler space photometry of V783 Cyg is too short
for a reliable nonlinear dynamical analysis aiming at the detection of chaos
from the Blazhko modulation. We estimate that two other stars could be suitable
for similar analysis in the Kepler sample and in the future TESS and PLATO may
provide additional candidates.
