Initially, it was said that the new cars required passing an updated inspection process before they could be released.
The origin of the delivery hold is reportedly related to the firmware (unofficially), but details remain unknown. It could be an additional check of settings or a firmware update.
"Update 7/23/21: Looks like several people have now reported that the hold has been LIFTED! And that we all should get our cars in the next couple of days!!! Someone mentioned it was a firmware update and that they needed to validate the cars."
Tesla's customers complained a little bit about the lack of communication, which is one of the company's trademarks actually.
Anyway, it's great to hear that the refreshed Model S has the green light again and that there was no serious hardware or EV-related issue that would cause a prolonged delay.
Both Model S Long Range and Model S Plaid should continue to populate the U.S. roads.
Hopefully the ramp-up will progress smoothly so the company will be able to sell 100,000 Model S/Model X units a year, just like in the best years of the pair, however the Model X is coming only in 2022 (at least that's the expected delivery time for new orders).
Meanwhile, those who already received the Model S enjoy its performance as we can see in videos and reviews.