basically the issue is described here:

https://stackoverflow.com/questions/57885790/valueerror-index-contains-duplicate-entries-cannot-reshape-pandas-datareader/59347328#59347328

I tried to download SP500 from yahoo. Following symbols (CBS, STI, VIAB) led to an unstacking error in pandas-datareader. To reproduce error download CBS and any other Symbol together for Dec 2019 as the error happen for Dec data (in case of CBS we have two values from yahoo for the 4th Dec).

Unstacking error doesn't appear when CBS is downloaded by its own.

Regards