Interesting high scattered PSI time series results

Hello everyone,
As can be seen from the attached time series, I obtained a time series in which the deformation fluctuates similarly at many PS points. The strange thing is that the deformation, which had high fluctuations until the middle of 2020, then stopped fluctuating.

Has anyone encountered such a problem before? What analysis strategies do you suggest to eliminate this error? Where could I be making a mistake?