Michael Schur shows that are left open-ended tend to get very bad about this, though to be fair it’s because they start so strong that the dropoff is more disappointing. The Office (US) and Parks & Rec both suffer from it in later seasons, and in my opinion P&R gets way too much of a pass for it. The Good Place was more tightly plotted, had various escape valves for weirdness, and ended before it got too far off the rails.