You’re SSL cert looks to be installed and working correctly from what I can see, so I don’t think it would be that causing the error. Did woocommerce provide any more detailed info other than “They suspect it’s the SSL cert that’s causing this.”? something more specific would be useful.
likewise “an unknown error” is a bit tricky to help with. can you provide as much information as possible, assuming we know nothing, about this error. Those who use woocommerce may know what the command “Woocommerce check out page” is, but I have no knowledge of this.
i.e. exactly what is the “development website”, exactly what are you doing when you get the error ( adding something to the cart ? making a payment ? … ). What exactly is the error ? (a blank page, you get a specific message … ) What is in the system logs at that time ?