I had the same thing happen to me mid-game today right before the chess.com servers went down. This wasn't discussed anywhere else I'm aware of, but I don't think the update is responsible - I think it might have something to do with the servers.
I haven't tried playing any games since then though, so I don't know if everything is "back to normal" again.
So I have figured out how to solve this problem, partly..
Now after the update the setting to turn on "Premoves" is in general settings. Go to "Home", then in the left bottom corner you will see the "Settings" button. There, choose "Live Games" and "Enable Premoves". However, after I have played a couple of games it had automatically switched off. By the way, I am having the same issue with "Always Promote to Queen". So I think it is a bug, not a feature 
. Maybe they will solve it in some time later. Hope it helped!
Hello,
Is the premove option disabled from blitz games? After an update I cannot make premoves and there is no such an option in settings. Sorry if this question was already discussed.