Continuity mistake: When Ser Barriston throws his armor and sword on the floor after being demoted, the sword stops by his armor. However when Sansa kneels down, the sword is now a good distance from the armor. (00:52:40)
Continuity mistake: When Catelyn meets up with Robb's forces, she hugs her son and then puts her hand on his shoulder/chest. In the next shot, her hand is down by her side. (00:41:40)
Continuity mistake: Arya and Syrio are practising at the start, we see them stop with their swords touching and crossed. Camera changes and Syrio's sword is much lower and no longer touching Arya's. (00:02:10)
Revealing mistake: Just after Jon is told he is confined to quarters, there is a shot of outside with snow falling. However the snow is actually rising. Indicating the shot has been reversed. (00:22:55)
Continuity mistake: Catelyn confronts her sister about the raven's message that arrived at dawn. When she does, the roll of paper is rolled completely differently between the 2 camera angles. (00:16:05)
Continuity mistake: When Ser Barriston throws his armour and sword on the floor after being demoted, the armor and sword are inside the black tiled square on the floor. Camera changes to show Sansa kneeling before the council and now the armor and sword are outside of the black tiled box despite no-one touching it. (00:52:30)
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 ★