The Magician - S3-E4
Revealing mistake: When Oliver meets Thea at the Grind and Jot Cafe (Which looks unsurprisingly like CC Jitters) you can see the cups on the table are from CC Jitters. (00:20:50)
Factual error: When the presidents are coming together, there are pictures being taken with flash photography, which would not be possible in a world without electricity. (00:34:15)
Nightmare on Christmas - S3-E22
Continuity mistake: When Power Man is wearing White Tiger's tiara (her Christmas gift), he has it on point-side down. White Tiger grabs it with both hands and puts it on and it's now point-side up, without her flipping it. You also see it go from a partial band tiara to a fully enclosed band tiara, like a crown.
Turtles All the Way Down - S1-E13
Other mistake: When Dr. Lee and Dr. Evans are arguing just after Red Reality Michael and Green Reality Michael converse, Michael turns around and says, "Shut up!" but the closed captioning says, "Enough!"
Factual error: When Susan is sorting Ruth's things, she finds Gordon's iPhone wrapped in a newspaper from 1994 with her voice-mail to him and realizes he went back in time, where Ruth killed him and took the phone from his corpse. Even if the phone had been turned off, after 16 years idle, the battery would have died long ago, but we see the phone is on with her message waiting. (00:55:50 - 00:56:45)
Split Second - S2-E2
Revealing mistake: Shortly after Kiera drives the van past the train tracks, we see a few different shots of Travis and Carlos fighting. In a couple of quick shots, Travis' stunt double can be seen. (00:13:00)