I think they were stuck on the task of getting him to explain what that evidence was (and what evidence the access he does have gives him), which in turn was complicated by his insistence that he wasn’t referring to a psychological fact of ease of conceivability.
komponisto and TheOtherDave appear to have been taking route 3. (challenging Richard’s purported access to evidence for zombie conceivaiblity).
I think they were stuck on the task of getting him to explain what that evidence was (and what evidence the access he does have gives him), which in turn was complicated by his insistence that he wasn’t referring to a psychological fact of ease of conceivability.