Problem Checking out - Authorize.Net payments

Hi, I am running Zencart version 1.5.5e using only the Authorize.net Aim module to collect payments. I have not made any changes to the default Responsive classic checkout pages other then cosmetic. I do require terms and conditions to be ticked on checkout. Ninety percent of the time there is no issue but I get occasional complaints that the customers cannot proceed past checkout page 3 and that when clicking on the continue button nothing will happen just dead. This will happen on Phones and PCs. Of note it will calculate the discount coupon and gift card balance entered but will not allow them to proceed past this page. When I check the logs there are not errors and when I check the Authorized.net logs there are not suspicious or failed transactions. I logged in as the customer and was able to checkout using COD checkout instead of a credit card with no issue and we are getting credit card orders before and after this customer attempted checkout. They tried many times and are a loyal regular customer so they are not new to the store. They are using a pc with Opera and tried it with Chrome as well. I am figuring they may not have entered the cc information correctly or ticked the terms and conditions but these would produce a warning message which they claim they are not getting any. I cant figure out how to troubleshoot this since I cant replicate it myself, has anyone else experienced anything like this? and what were your resolutions or troubleshooting steps.

So after much testing and remote desktop into my customers computers i was able to finally reproduce the issue as follows

If you have: My Store/PA-DSS Ajax Checkout? = true (which you should)
and you have the payment module COD also enabled and possibly other modules(didn't test)

and your customer fails to enter the cc number correctly(misses a number) they will not be able to proceed and they will not get any warning messages just a dead continue button, this happens in all browsers and phones and tablets we tested them all.

If you disable either of the above and refresh the cache Ctrl-F5 they will get the warning message(if information is still wrong) and be able to checkout(if information is corrected)

Disabling My Store/PA-DSS Ajax Checkout? will allow you to have other modules running and work correctly.

Its hard to believe no one else has experienced it but it took me months to realize it because I only activate COD if I need to check out without a credit card. It will work ninety percent of the time since most people will enter the information correctly but it will lockup the whole checkout process if they don't

Is this issue fixed in versions after this 1.55f, 1.56, 1,56a ??