Often getting 0 tweets for no apparent reason

Does anyone have experience where often they are getting 0 tweets returned to them, and for no apparent reason? I am getting this periodically, for example currently with the code below.

---
import got
from datetime import datetime, timedelta
import datetime
import pickle

handle = '@southwestair' #twitter handle

#declare global variables
n = 50 #max number of tweets to collect (500)
d = 10 #past d days (365)
#dd = date.today()
dd = datetime.date(2017, 01, 06) #date from (going backwards)

k = 0

dt = dd - timedelta(k)
df = dd - timedelta(k + 1)

print("DAY")
print(df)

df.strftime('%m/%d/%Y')
df = str(df)
print("DATE")
print(df)

dt.strftime('%m/%d/%Y')
dt = str(dt)

tweetCriteria = got.manager.TweetCriteria().setQuerySearch(handle).setSince(df).setUntil(dt).setMaxTweets(n)
curtweets = got.manager.TweetManager.getTweets(tweetCriteria)
print("# TWEETS")
print(len(curtweets))