APM CRLDP - verify signature

Hello,

I'm using machine cert checker with crldp for http using the method described in this post.

https://devcentral.f5.com/questions/machine-certificate-revocation-checks

Everything appears to work as expected except I get a failure when the 'verify signature' is checked. I assume this is the signature on the CRL? but this is issued by the same CA as the machine cert and there doesn't appear to be any configuration options apart from the checkbox, any ideas what I'm missing?

thankyou