When Nancy is fleeing Vecna in the Upside Down lab, she rips some wooden planks off a corridor door to escape. However, it's a swinging door so all she had to do was simply push it open and slip between the planks. When she does push open the door and enters the next room, the same door now has a handle on it.
When Dr. Brenner emerges from the bunker, everything is silent. Then, when he is shot at, the helicopter blades become audible. Helicopters are very loud and cannot sneak up on people like this.
At 54:53 in, the military vehicles going up to the bunker are common for era, except there is a Humvee which only debuted in the US Army in 1989, and this was supposed to be 1986.
When Jonathan reaches the bunker and accelerates, a shot of the speedometer is shown; for some reason, the trip odometer is showing 0.0 miles even though they have been driving all day. It's possible that Jonathan hit the reset button but he would have no reason to do so.
In 1986, no one would say they "typed" the phone number wrong. They would say they "dialed" the number wrong even if it was a push button phone.
Joyce gives a phone number beginning with area code 775. The state of Nevada had only one area code (702) until 1998, when 775 was created for northern Nevada, relegating 702 to the Las Vegas area only.
The US military didn't start using Humvees until 1989.
When Antonov is on the phone to call the US, he asks Joyce for the phone number. The area code she gave was 775, however, prior to 1995, all area codes in the US had either a 1 or a 0 as the middle digit.
Season 2 Demodogs resisted a barrage of assault rifle fire without flinching, while the Demodog at Kamchatka immediately dies after a single pistol shot.
When the soldiers raid the bunker, none of them brings torches or affixes torches to their weapons; although this makes for a more dramatically-lit firefight, it makes no sense if you are planning on raiding an underground facility.