Whether it be (https://industrialscripts.com/bad-writing/) plot holes (https://www.buzzfeed.com/elliewoodward/infuriating-plot-holes-tv-shows), character assassinations (https://www.pajiba.com/tv_reviews/is-this-the-biggest-tv-character-assassination-this-year.php), inconsistencies (https://www.buzzfeed.com/hanifahrahman/tv-inconsistencies), and just undoing all of the stakes and world building.

Two Broke Girls
Full House
My Mother The Car
Baby Talk

These are just a few off the top of my head that were poorly written from the beginning. Other shows like Happy Days and The Andy Griffith Show started out strong, but started declining in the later seasons.

She's the Sheriff
Three's Company
Saved By the Bell: The New Class
Baby Talk
Cavemen
Small Wonder
Mr. Smith (the show starring an orangutan)

The Lost Episodes of The Honeymooners showed a lack of continuity. Alice has a lot of different relatives throughout the run and how the Kramdens and Nortons met was unclear.