The Contest - S1-E24
Other mistake: When Tom unzips the backpack to collect everyone's devices, he adds a few devices that belong to Ben, and as Tom drops in sneaky Ben's last device, watch as the backpack zips itself shut mid-shot, all on its own. (00:04:32)
Revealing mistake: When Iris is sitting in bed recording the message for Barry, she is holding her iPhone so that the start button is on the left side, but the "video record" button appears on the right. Additionally, her right hand covers the speaker area of the phone fully, including the front facing camera. It is impossible for Iris to be recording the video live and reveals that the video footage was recorded ahead of time. The illusion that the video is being recorded by Iris live is further ruined by the fact that the room lighting is turned off in the scene, but the recording is well lit. (00:02:55)
Continuity mistake: Right before Meliodas punches Hendrickson, Meliodas holds the dagger in his left hand, but it switches to his right hand in the next shot. (00:22:06)