When i try to create a DataFramne from a List of Lists it shows 16 empty columns that i have no idea where they come from

Question

Im trying to create a dataframe with a list that contains data about a message as lists, having date,sender and body of the message

 def extract_data(text): 
   fields = []
   fields = text.split(']')
   fields[0] = fields[0][1:]
   fields[0] = fields[0].replace('/','-')
   fields.extend(fields[1].split(':'))
   fields.pop(1)
   return fields

lines = []
messages = []
header = ['Date','Sender','Body']
with open('merlinator.txt',encoding = 'utf8') as f:
    for line in f:
        if has_date(line):
            lines.append(((line.replace('\u200e','')).strip('\n')))
        else:
            lines[len(lines) - 1] += ' ' + line.strip('\n')

lines = [l for l in lines if valid_user(l)]  

if i append just one item to the list "messages" and use it to create the df, it works just fine.

lines = [l for l in lines if valid_user(l)]   

messages.append(extract_data(lines[0]))

df = pd.DataFrame(messages,columns=header)
df

enter image description here

if i use a loop to complete the list i´ll use for the dataframe, it appears to be fine when displayed, but when used to create the dataframe it shows 16 empty extra columns.

for x in lines:
    messages.append(extract_data(x))

df = pd.DataFrame(messages)
df

enter image description here

what im i doing wrong?

pd: Im learning python and pandas so every constructive criticism about my code is morew than welcome, also english is not my first language so sorry for bad english :)

EDIT

the input file is a whatsapp group chat exported as a .txt and it looks like this:

    [01/12/2019 4:01:38 AM] Joaquin Cibeira: He creado este grupo con el fin de que nadie nunca mas se pierda una juntada
    [01/12/2019 4:01:57 AM] Joaquin Cibeira: Si consideran que falta alguien, ej: marinita. Lo metemos
    ‎[01/12/2019 4:03:30 AM] Almada: ‎sticker omitted
    [01/12/2019 4:03:35 AM] ‎You added Juani Pisa
    ‎[01/12/2019 4:04:16 AM] Juani Pisa: ‎sticker omitted
    ‎[01/12/2019 4:05:12 AM] Almada: ‎audio omitted