Breaking the ADGVX cipher using the Index of Coincidence for the transposition key

To break the ADFGVX cipher, I've found that you need to find the transposition key first, apply that, and see if it works with monoalphabetic substitution. The transposition key is found through using hillclimbing with IOC and finding which keys give the best IOC. However, the script does not always seem to accurately give the key, even when trying to iterate through the 10 best keys it finds. Have I missed something here, or is there a better way to do this? Here is the function I use to find the key

def HillClimbingTransposition(text, key, bestiocs, bestkeys,iterations):
bestioc = -99
besttext = text
keylength = len(key)
iteration = 0
while iteration < iterations:
    iteration += 1
    #print(iteration)
    newkey = key[:]
    RandomNumber1 = (random.randrange(keylength))
    RandomNumber2 = (random.randrange(keylength))

    a, b = RandomNumber1, RandomNumber2
    newkey[a], newkey[b] = newkey[b], newkey[a]

    newstring = DecryptTransposition(text, newkey)

    ioc = IOC(newstring)

    if ioc > bestioc:
        bestioc = ioc
        key = newkey
        besttext = newstring
        #print(iteration)
        iteration = 0

    if ioc > min(bestiocs) and key not in bestkeys:

        #besttransposition = bestkey[1]
        index = bestiocs.index(min(bestiocs))
        bestiocs[index] = ioc
        bestkeys[index] = key
        #print(bestiocs)
        #print(bestkeys)
return (besttext, key, bestiocs, bestkeys)

the full repl link is https://replit.com/@creeperthecat/ADFGVX-Cipher#main.py