Continuity mistake: The difference between the heights of Ser Jaime and Lady Brianne continually differs. Sometimes Brianne is taller than Jaime by several inches, and at other times they appear to be nearly the same height when standing side-by-side, even though they're always wearing the same clothes and boots.
Continuity mistake: This is when the family is watching Bran practicing archery. The round target on the left has a large hole on the bottom right side, presumably from a previous arrow. This hole moves around throughout the scene, most noticeably in the shot after Arya shoots an arrow right into the middle of the target. (00:10:40)
Continuity mistake: When we see the dead deer at the start there are maggotts all over the face of the deer. Between camera angles, the position of the maggots differ drastically. (00:15:00)
Continuity mistake: Ser Jorah has just given Daenerys 3 books as her wedding present. As she takes them, their spines are pointing towards her right side. Cut to the next shot, as Jorah informs her that he served her father, the spines are now pointing towards her left side. (00:50:45)
Continuity mistake: At Daenerys' wedding we see a man get sliced across his midriff and lean backwards with his mouth open. Camera does an instant cut and now he is slouched forwards. (00:52:00)
Continuity mistake: Khal Drogo has just lifted Daenerys onto her horse after their wedding celebration. Her hair is behind both shoulders. In the immediate next shot, her hair has now moved in front. (00:55:00)
Continuity mistake: When Ned executes the deserter, the wide leather straps of Ned's cloak are crisscrossed with his left over his right. But when Ned walks over to Bran, the straps are now crisscrossed the opposite way. Not due to flipped shots.
Continuity mistake: When King Robert arrives at Winterfell, the wide leather straps of his cloak are crisscrossed with his left over his right, but when Robert and Ned walk inside the crypts, Robert's straps are crisscrossed the opposite way, with his right over his left. The shots are not flipped.
Continuity mistake: When Ser Jorah tells Dany that her life with Khal Drogo "will get easier," watch the strap of her dress. It moves up and down her right shoulder throughout the scene. (00:03:05)
Continuity mistake: When Tyrion is talking to Sandor, his position in relation to the gate changes between camera cuts. In the first shot he is next to the gate. In the second shot he is about 3ft away. (00:06:20)
Audio problem: When Tyrion is saying he wants to stand on top of the wall, it is an over the shoulder shot, however his mouth doesn't match up with what he is saying. (00:07:40)
Revealing mistake: When we see Joffrey get attacked by the dire-wolf, You can see his arm suddenly has padding underneath his jacket. (00:47:20)
Cripples, Bastards, and Broken Things - S1-E4
Continuity mistake: When Ned and Petyr are walking and talking about Sir Hugh of the Vale, they pass a wheelbarrow while walking in a straight line that simply vanishes from the side of the path. (00:28:05)
Cripples, Bastards, and Broken Things - S1-E4
Continuity mistake: When Ned and Petyr are walking and talking about Sir Hugh of the Vale, they are in brilliant sunshine in one shot then in an instant cut there is no sun. (00:28:05)
Continuity mistake: After the attack on Catelyn we see Bran Luwin and Theon talking while Theon is practising archery, the arrows in the board are constantly changing position and appearing and disappearing with no time to do so. (00:13:50)
Continuity mistake: When Bran is asking about where his mother has gone he is playing with a lure. Between instant cuts the position of the lure in his hand is constantly changing. (00:15:20)
Continuity mistake: When Bran is taken from his horse in the woods, there are 3 wildlings that attack. The first Rob cuts his throat, the second, Rob is holding the female wildling by the hair, he then spears and kills the third with his sword and the very next frame the 3rd wildling is then holding a knife to Bran's throat, unharmed. (00:11:15)
Continuity mistake: When Tyrion wakes up inside the skycell you can see two skylights in the ceiling of the cell through which the sunlight passes. However, when we get a long shot of the skycells, you can see there's no way for the light to pass through them, as there are no "holes" on the floor of the cells above Tyrion's. (00:13:45)
Continuity mistake: When the guard is hitting Tyrion in the sky cell, Tyrion has his arms outstretched in one shot and against the wall in the next. (00:14:00)
Chosen answer: Considering the show was in production for nearly a decade, it is hardly surprising that many characters were recast. Actors constantly move on to other jobs, creating scheduling conflicts. Some may not want to be tied to one project for so long a period, particularly for relatively minor roles that paid little money. As some characters became more prominent, the producers did recast a few roles with better-known actors. For example, Max Von Sydow replaced the actor who originally played the Three-eyed Raven. Some actors voluntarily left for personal reasons. Jennifer Ehle was originally cast to play Catelyn Stark but dropped out because she'd recently given birth. Other actors claimed they were replaced for "political" reasons. Here is a website with a rundown of which actors were replaced and why: https://screenrant.com/game-thrones-characters-recast-new-actors-every-why/.
raywest ★