Connected old generation to a new TV, and 4th gen. too.
On old one, went to schedule to change each to none. Not an option.
Have to go to live TV, 11 days from today, find it and chose do not record.
Legacy user here. I have noticed sometimes the UI is slow to update. I suspect that was your problem. I have deleted (or recorded) shows and it doesn’t update right away.
FWIW, for legacy Tablo the mobile Android app is much slower in updating than my Roku devices.