Checkout errors related to ezapps extension

[sloth456]

We have ezapps zoom installed and we also use sagepay to process our payments.

The error we get is that some customers finish their sagepay order and then they are not redirected to the success page, therefore no order is logged in magento but we still receive payment.

The customer usually thinks the order has not gone through successfully and tries to pay again.

This error does not occur when zoom cache is disabled.

The error does not happen in 100% of cases, but still happens fairly regularly.

The error was much more prevalent when we had SIDs in our URLs. We have not disabled SIDs but we have eliminated most causes for SIDs appearing (by redirecting all www URLs to our base URL which uses the non-www version). Since doing this the error doesn't happen as often.

I have not been able to replicate the error myself, so I'm a bit lost on how to fix it. The only thing I can say is that I think it is related to how zoom handles sessions and SIDs.