I experience similar frustration. I'm not sure, but it seems that for the "last game" if there is not enough arena time the game is aborted and doesn't count. But there doesn't seem to be a penalty if the losing player aborts the game in that time-frame.
What I tend to do is just not play the last game. I don't know if it's a good strategy, but I find myself less frustrated.
KK
What I have been doing near the end of an arena tournament is
When Arena is near ending, players may opt to abort the game by not moving so long as they have enough time. This opponent had 1.4 seconds left when Arena ended. I had premoved my last two moves when there were five minutes left, but I knew that it would be close.
I'm not sure that I'm complaining. I've benefitted from this feature in similar circumstances. It is a feature of how chessdotcom designed the site. On another site, games finish but no longer count towards the Arena score. That means that you are stuck in the game until you resign or finish another way. You cannot join another game or event.
Chessdotcom made a choice. We live with it.
But, when a player has premoved checkmate, ...