We have integrated our application with Auth0, and previously, validations such as blocked user checks were working correctly. We are using the following Lock file:
From the error message that you have posted, it appears that the certificate that you are using to sign the assertion element might be used for a different response element than the one intended or you might be using the wrong certificate.
I would recommend to use https://www.samltool.com/ or https://samltool.io/ (which is provided by Auth0) in order to validate the XML file used for your SAML connection. Also, check for any add-ons which might be modifying the output.
Regarding this error, you can check out the following posts as well: