Yeah, same thing happened to me, 2 times! I don't remember the first game, but I have the 2nd game! Here's that game: https://www.chess.com/live/game/3434828296 I premoved the mate, but after a few of them played out, the rest didn't!
Premoves disappearing and inability to move
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You didn't lose. It was a timeout with insufficient material draw.
Looks like things froze up with almost 10 seconds left.
I know I didn't lose, I had mate premoved against a 2300 with almost ten seconds left and I flagged.
Feb 16, 2019
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#8
Stephen_Stanfield wrote:
I know I didn't lose, I had mate premoved against a 2300 with almost ten seconds left and I flagged.
Same for me, but my opponent was a GM, 2800+ 
Feb 19, 2019
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#9
If I remember right, you can only queue up eight premoves. Did you maybe exceed that?
Feb 20, 2019
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#10
I don't think there's any way to exceed that, since it doesn't let you premove after the max is reached
The max is 8? You're most probably right, then I premoved 6-8 moves, and the last 4 weren't played out
Feb 21, 2019
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#11
I can't see why you need premove at the end: you have 10 seconds. It may be you had an unfortunate snarl up / connection problem that got in the way of a win that you would have got.
Once my time flashed under 20 seconds I stopped looking at it and focused on converting the ending as fast as I could. I didn't realize how much time I had left until my pieces stopped moving. Oh well, at least it wasn't rated. (though I would still have gained rating)
I was winning this game (https://www.chess.com/live/game/3462350834) and premoved the unstoppable mating sequence and waited. But only a few of them were played, the other premoves disappeared. I also could not move my pieces and had only 9 seconds left. What caused my premoves to go away? What prevented me from moving my pieces? I don't know if it was my mouse, connection or chess.com that cost me that win but I don't want it to happen again! Any advice about this would be appreciated.