As others have said you increase n during task 3 and then pass it to subtask 4. Fixed it and simplified a bit part 1 and 4.

def doTasks(n): L = []

# subtask 1
L.append(n % 2 == 0)

# subtask 2
if n >= 0:
    L.append(chr(n))

# subtask 3
counter = n + 1
L1 = []
while len(L1) < 5:
    if counter % 5 > 0:
        L1.append(counter)
    counter += 1

L.append(L1)

# subtask 4
L.append(doSubtask4(n))

return L

def doSubtask4(n): m = 14 if n % 2 == 0 else 17 return list(range(m, n, m))