When the gang is sitting around discussing if anyone thought that Chandler may have been gay, Rachel talks about meeting Chandler for the first time thinking he might be when she arrived and the series had started, but later on in the series on several occasions during flashbacks, Chandler and Ross both knew Rachel in high school and she and Chandler had actually kissed at a college party. Also, in this episode Joey claims that he didn't think Chandler was gay the first time they met, but in The One with the Flashback (1996), when Joey and Chandler meet, Joey says "Oh and I'm totally fine with it's the whole gay thing."
At the funeral reception when Monica and her mom, Judy, are talking on the couch, the amount of wine in their glasses is not consistent. It goes down, up, back down, and back up between shots.
A medical doctor, and not a nurse, should give the news of the passing of the patient after examining them, to avoid the confusion.
The heart monitor is heard when the patient "comes back to life" but it was never hooked on Nana.
When Ross is in Nana's closet and brings down the cascade of Sweet and Lows, they sprinkle down like rain from directly above him. He was reaching forward, so they should have fallen from in front of him and all at once. Obviously, there's a technician off stage dropping the Sweet and Low packets.
In any hospital, an end of life patient would be surrounded by family in the room, not waiting outside.
Ross and Monica are Jewish so they should have given Nana a Jewish funeral, followed by a Shiva. However, it is possible that Nana was not Jewish, and that their mother, Judy, converted to Judaism after marrying their father, Jack Geller.
Correction : Monica and Ross are part Jewish ( Ross says it in the one with the holiday Armadillo), so it seems like their mother and her family aren't Jewish, and it is not clear whether or not she converted to Judaism in order to marry Jack. If she had converted, wouldn't the kids be fully Jewish?
So it is not an error that her mother Althea had a non Jewish funeral.