time series - what is the possible timeseries problem that might have caused this plot?

Question

what is the possible timeseries problem that might have caused this plot? Every 22 months the data collected seems to be going up or down alternatively.

question from:https://stackoverflow.com/questions/65868598/what-is-the-possible-timeseries-problem-that-might-have-caused-this-plot

Answer 1

Waitting for answers