Factual error: When they go to 1954, the hamburger drive in says it has frappes. Not invented till '57, and not in the US public eye until at least 45 years later.
Suggested correction: What you're describing is a Greek café frappé made with instant coffee. In New England "Frappe" is what many would consider a milkshake with ice cream in it, and has been around since at least the 50's (Vic's dad even mentions getting frappes in episode 4).
Factual error: At the end when Skeksis enters the crystal chamber, in the overhead shot you can see 22 arcane symbols around the crystal when there should only be 18, one for each exiled skeksis. (00:45:53)
Welcome to Hotel del Luna - S1-E1
Factual error: The dead policewoman removes the bullet that she was shot in the head with. The bullet appears to be completely intact and undamaged as if never fired. Real bullets that have been fired into something or someone do not appear like this. (00:36:30)
Pride Parade - S5-E3
Factual error: Nandor manages to fly up to space, then loses control and falls back to earth in a fireball as he reenters the atmosphere. But objects reentering the atmosphere only get hot because they're generally travelling at immense speeds, 7-12 kilometers per second. Nandor just floated straight up, then falls straight back down. When Felix Baumgartner parachuted from the edge of space his maximum speed was about 1,300 km/h, and he didn't catch fire.