I was working with your historic data of Brazilian Stocks and came across a stock with a lot of missing data or the same prices throughout the days. The stock is BCFF11.SA (https://finance.yahoo.com/quote/BCFF11.SA/history?p=BCFF11.SA).
I hope you can fix it.
Thanks for the great job, have a nice day!
Mi Po commented
Problem is for many other stocks e.g. most popular:
Missing many rows in Historical data section since Feb 21, 2020 to today all cells of table are empty (no values)
Yahoo finance is now not usable, missing many data, charts are incorrect!
See broken chart (straight line) here: https://i.ibb.co/yW7rwYs/broken-chart.png