When Matthew is climbing up the ladder and Grace speaks to him out of her window, his left hand is alternately on/off the rung between shots.
The level of Grace's wine when she's talking to her late husband's lover. It goes from half to almost full as the camera switches from a side to a behind view. Also, when the wine is poured, the bottle is not tipped up long enough and it doesn't make a long enough pouring sound to put that much wine in the glass.
When Grace is cleaning up in the kitchen and talking to Harvey after the funeral, a mishap between them causing an empty plate to smash on the floor after she just picked up two stacked plates with left-overs from the table. In the next two close-up shots she doesn't set down those plates, but in the following wider shot as she picks up the pieces and stands up, they are back on the table and she picks them up again.
In the scene where Quentin is in the village shop asking for directions, the reflection of the boom mic is visible in the mirror.