_pickle.UnpicklingError: unpickling stack underflow

This error occurs when the unpickling process encounters a pickle data stream that does not contain enough information to properly recreate the original object. Specifically, it means that the stack of data that is being used to reconstruct the object is empty or has fewer items than expected.

Possible causes of this error include:

1. The pickle data stream is corrupted or incomplete.
2. The object being unpickled was pickled using a different protocol or implementation than the one being used for unpickling.
3. The object being unpickled has changed since it was pickled, and the new version is not compatible with the old version.
4. There is a bug in the pickling or unpickling code.

To fix this error, you may need to examine the pickle data stream and determine if it is corrupted or incomplete. If so, you may need to regenerate the pickle data. If the error persists, you may need to modify the pickling or unpickling code to ensure compatibility between different versions of the object.