Two major issues came up during my stay: 1) The heating radiators in the unit did not work at all and 2) the door to the unit did not lock.
When I realized that the heaters were not working, I called Gene immediately. This was at 6:50pm on the day of my arrival (i.e., not an unreasonable hour). I asked him if the heaters had been working before and he said "I have no idea, to be honest" and then asked if he could call me back later that night. Our call lasted 32 seconds. He never called me back. He supposedly lives nearby the unit, but did not offer to come over to help deal with any of this in person. I did find two small (~8 inch) space heaters in the apartment which provided some heat. In the "other things to note" section at the very end of the listing, Gene does mention "If cold, ask about a space heater!" but does not specify that the reason why this is necessary is because the heating in the unit doesn't work.
The following day, I realized that although the door to the outside locks, the door from the shared stairwell of this apartment building into my unit did not lock. There was a key code for entry, but you could open the door without entering the code. I could lock the door manually from the inside using the deadbolt, but it would not lock when I left the apartment for the day. Since calling Gene hadn't worked, I sent him a message about this significant security issue. That was 3 days ago now and he has not responded.
Otherwise, the apartment was fine, but future airbnb users should be aware of these fundamental issues with host responsiveness, heating, and security before deciding to book a stay here. I've stayed in a number of airbnbs before and have never left less than a 5 star review, so this is definitely an outlier.