Revealing mistake: When Johnny shows up to Cobra Kai dojo and all the kids are there. In the video playback they show on the phone you can see Miguel didn't land the kick, and the kid just fell down. (00:28:18)
Revealing mistake: When Mitsuhashi and Ito meet on the first day of school, the clock in the classroom never advances from the 8:20 position despite the scene taking place in a span longer than one minute. (00:04:45 - 00:06:08)