Some ETF Tickers Not Working in Yahoo Finance DataReader

I'm gathering data from a bunch of ETFs through Yahoo Finance using Pandas-Datareader and I'm getting odd errors with a handful of the tickers even though the data seems available. The code is very simple:

start = datetime.datetime(2010, 1, 1)
end = datetime.datetime(2017,1,1)

for ticker in TICKERS:
     f = dr.DataReader(ticker, 'yahoo', start, end)

and works for most of my tickers but not all:

EMLP GDVD (Failed to get data for GDVD) AMZA RFDI ARKK ARKW SECT (Failed to get data for SECT)

EMLP works fine. Datareader produces urls like this url for GDVD even though the historical data for GDVD is available on the website. I see the following error in Chrome using the GDVD url:

{"finance": {"error": {"code": "Unauthorized","description": "Invalid cookie"}}}

Is there a way to get historical prices for these tickers? The full list of failed tickers in case anyone can see a pattern:

 ['GDVD', 'SECT', 'DWLD', 'CCOR', 'DFNL', 'DUSA', 'AIEQ', 'CACG', 'QSY', 'ACT', 'TAXR', 'TTAI', 'FLIO', 'FMDG', 'VGFO', 'FFSG', 'LRGE', 'YLDE', 'VESH', 'DEMS', 'SQZZ']