What If... Captain Carter Were the First Avenger? - S1-E1
Deliberate mistake: When Peggy and Steve are studying the map where the 107th Army division is held captive, the names on the map are nonsensical names that do not even follow German spelling or standards for place names ("Farfignugen," "Dädtenorth," and "Rosskjhberg," for instance). Most of them are also reused, appearing several times on the same map. This is most likely done deliberately so as to avoid any resemblance to real places, but still looks out of place and illogical. (00:11:27)
Just Let Go - S1-E4
Deliberate mistake: When Devon does an internet search for Chucky, pictures of Tiffany and Nica pop up. But they're still-shots from "Bride of Chucky" and "Cult of Chucky." It makes no sense that they'd be in an internet search - nobody could have taken those photos.