Continuity mistake: After Kellijian aims to choke his wife, they kiss. Right afterwards, the position of her left arm on his body is not continuous between shots.
Continuity mistake: When Jessica talks to Lt. Bergkamp, she takes her left hand to her ear to improve her hearing, but from the opposite shot, her hand is lowered.
Continuity mistake: Before Joan leaves the restaurant, she has a glass of wine on her right, but from Jessica's POV, the glass has moved to Joan's left side. Also, Jessica's glass is in front of her, but moves to the right side of the table after Joan leaves.
Continuity mistake: When Bud and Andy arrive at Cagliostro's table, Jessica stares with her glasses on, while Joan turns her head around. An instant cut later, Jessica's glasses are off and Joan is turning her head again.
Continuity mistake: When Jessica is having dinner with Joan, Jessica's right arm is either extended on the table next to the cutlery or not, depending on the shot.
Continuity mistake: When Joan leaves the restaurant, her glass is full. Next time we see it, it's empty.
Answer: The storyline was that Jessica was teaching classes in New York. However, after so many seasons and as ratings declined, it was probably to freshen up the series with a different locale, introduce new characters, and have a greater variety of situations in which Jessica could solve murders. It was already unbelievable that so many people could be murdered in the small town of Cabot Cove. Being in a large city like New York makes it a tiny bit more plausible.
raywest ★