Barry is shown throwing lightning during his flashback battle with Hartley. However, he didn't learn that ability until Season 2, and the flashback is set during Season 1.
This could be written off as Barry having learned the power earlier in the new, post-Crisis time-line.
The establishing shot for STAR Labs after Barry and Nash meet with Hartley is reversed, as indicated by the backwards text on the sign.
Kamilla decides to trust Iris after Iris tells her something that supposedly no one else could know. Iris's mirror duplicate fooled everyone for over a month, indicating she knew everything Iris knew.
Cisco calls Pied Piper's henchman his "band of merry men". In traditional English literature and folklore, it was always Robin Hood and his band of merry men, not the Piper.