Two Swords - S4-E1
Continuity mistake: When Arya and Hound come upon the murdered people Arya is riding facing left. After they pass, she is facing right. (00:48:40)
The Mountain and the Viper - S4-E8
Continuity mistake: When Oberyn first tells Gregor that he will make him confess to raping and killing his sister Elia and her children, he is holding his spear with both hands. In the next shot, he's holding it with just one hand.
The Watchers on the Wall - S4-E9
Revealing mistake: Castle Black defenders drop heavy stones on the free folk and one of them gets hit on the head but forgets to act injured (or dead). (00:23:20)
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 ★