Continuity mistake: When Drogon comes flying over the hill, he overtakes the front of the Dothraki line in the shot where he roars, but in the next shot, he's behind the line again.
Continuity mistake: In order to save him from Drogon's fire at the very end of the episode Jaime is thrust by Bronn into water about 40 feet deep. This shouldn't have been possible especially after Jamie is shown galloping on his horse along the watery beach side just moments before.
Suggested correction: As shown in the following episode, the undercurrents had carried them some distance down-river.
An undercurrent may explain how they eventually got to the other side of the lake but not why the water on the shore became so deep so quickly.