Hi Tracey, when we were load testing Kentico, we came up with a workaround - you can disable the hash validation by using the web.config key:
<add key="CMSEnableHash" value="false" />
At first, we used the same code for generating hash in the load testing tool, so the hash validation worked, but it was not maintainable enough and we decided to create that workaround instead.
Please note that it's just a workaround and shouldn't be used in the production since it brings a security risk.
Does it work for you for testing purposes?