In the reactor room fight scene, when Martian Manhunter is pinned by Armek and being choked, M'gann stabs him and he falls to J'onn's left. Seconds later, after shifting back to his human form, there is no body next to J'onn as he gets up, ... or behind him where one of the white Martians suddenly pops up.
During the conversation between M'gann M'orzz and J'onn J'onzz in the DEO corridor after Winn stabilizes the reactor the white garment label for M'gann's sweater is visible, but the label is not visible as she turns away following the conversation.
During the scene between J'onn and M'gann at the end of the episode (which covers a continuous timespan of around a minute), close-ups of J'onn's wristwatch go from 7:05, to 8:15, to 7:20.
When Winn stabilizes the reactor core, in the message that appears on the monitor, Stabilized is misspelled.