Runs sometimes and sometimes gives an index error

I want to make a program that randomly simulates the flow of a champions league tournament (football/soccer tournament). The format of the tournament is as follows:

1. There are 32 teams that qualify each year.
2. The teams are then randomly distributed into 8 groups containing 4 teams each.
3. The teams all play each other and 2 of the best performing ones qualify to the next round (round of sixteen)
4. The matchups are decided by randomly selecting the teams 2 at a time with the constraint that no two teams from the same group may face each other again
5. The winner then progresses to the next stage and so on and so forth until we have a winner.

In my program I have tried to implement this format using the random module in python. However, once every 4-5 iterations I get an index error at either the round of 16 selection step or the quarter final selection step. I cant seem to understand why. Please help

import random

teams = ["Barcelona", "Atlético Madrid", "Real Madrid", "Valencia", "Manchester City", "Liverpool", "Chelsea", "Tottenham Hotspur", "Juventus", "Napoli", "Atalanta", "Internazionale Milano", "Bayern München", "Borussia Dortmund", "RB Leipzig", "Bayer Leverkusen", "Paris Saint-Germain", "LOSC Lille", "Lyon", "Zenit", "Lokomotiv Moskva", "Benfica", "Shakhtar Donetsk", "Genk", "Club Brugge", "Galatasaray", "Salzburg", "Slavia Praha", "Ajax", "Olympiacos", "GNK Dinamo", "Crvena zvezda"]

random.shuffle(teams) #shuffling the 32 teams

Group_A = []  #making empty lists of all 8 groups
Group_B = []
Group_C = []
Group_D = []
Group_E = []
Group_F = []
Group_G = []
Group_H = []

for i in range(32): #using for loop to add each of the 32 teams in group lists
    if i <=3:
        Group_A.append(teams[i])
    elif i <=7 and i>3:
        Group_B.append(teams[i])
    elif i <=11 and i>7:
        Group_C.append(teams[i])
    elif i <=15 and i>11:
        Group_D.append(teams[i])
    elif i <=19 and i>15:
        Group_E.append(teams[i])
    elif i <=23 and i>19:
        Group_F.append(teams[i])
    elif i <=27 and i>23:
        Group_G.append(teams[i])
    else:
        Group_H.append(teams[i])

GroupDict = [Group_A, Group_B, Group_C, Group_D, Group_E, Group_F, Group_G, Group_H]

#adding all group lists to another list

print("Group A:\n", Group_A) #displaying group stage draws
print("Group B:\n", Group_B)
print("Group C:\n", Group_C)
print("Group D:\n", Group_D)
print("Group E:\n", Group_E)
print("Group F:\n", Group_F)
print("Group G:\n", Group_G)
print("Group H:\n", Group_H)

r16 = [] #making empty list for the round of sixteen

for i in range(8):         #randomly selecting 2 winners from each group and adding
    list = GroupDict[i]    #and adding them to r16 list 2 at a time
    n = 2
    r16.append(random.sample(list, n))

print("\n\nTeams that qualified to the round of 16:",r16)
r16_matches = [] #making an empty list to store randomised matchups

for i in range(16):           #code to select 2 random teams with
    t = random.choice(r16)    #the constraint that no two teams from
    if not t:                 #the same group may face each other again
        continue
    else:
        t1 = random.choice(t)
        t.remove(t1)
    while (1==1):
        s = random.choice(r16)
        if not s:
            continue
        else:
            if r16.index(s) != r16.index(t):
                t2 = random.choice(s)
                s.remove(t2)
                break
            else:
                continue
    match = [t1,t2]
    r16_matches.append(match)

print("\n\nRound of 16 matchups:", r16_matches, "\n\n")

Qfinals = []
Even = [0,2,4,6]

for j in Even: #selecting one winner from each round of sixteen matchup and putting them together, 2 at a time
    qt1 = random.choice(r16_matches[j])
    qt2 = random.choice(r16_matches[j+1])
    qm = [qt1, qt2]
    Qfinals.append(qm)

for l in range(4):
    print("Quarter final ",l+1," : ",Qfinals[l][0], " vs ",Qfinals[l][1])

Sfinals = []

for k in range(4): #selecting a team from each quarter final matchup to face in semifinals, 2 at a time
    S = random.choice(Qfinals[k])
    Sfinals.append(S)

print("\n\nSemi Final teams:", Sfinals)

ft1l = [Sfinals[0], Sfinals[1]]
ft2l = [Sfinals[2], Sfinals[3]]

finals = [random.choice(ft1l), random.choice(ft2l)] #selecting random winner from each semi final

print("\n\nFinals: ", finals) #printing finals

print("\n\nWinner: ", random.choice(finals)) #randomly selecting winner from final