I had a bit of a dig into this, and if we follow the trail there should be enrichment:
It starts from emailer here and then it calls the user notification extension which enriches with the user email here and then passes it to the build email helper here and finally sets the address in the message builder here before sending it.
Aside from that the chat summary email already works on other sites so there is likely something else that is causing an issue here.
I think an interim solution is to pass the user email to the job which should give us a bit more confidence/visibility that the correct data is there from the outset: