It might have been a reset, or u might have, on accident, gotten confused with 10 min and 1|0 min. It has happened to me sometimes but I just abort... Hope this helps
Live Chess Defaults to 10 Minutes?

It's not my settings. I've never seen it happen. So weird. I'm used to just clicking "Play" to play.

I don't know if that preference is stored in the DB or a cookie. If it is the latter, if your cookies for the site get deleted, it would reset to defaults.
Just create a new custom challenge at your chosen time control and the next time just hitting play should default to that.
I have exactly the same problem but only since yesterday. I posted on the forumbut it has not shown up??? Is it a new policy by chesscom to make us play longer games? How do i change it back!!???

For post 5 and 6. What happens when you create a custom challenge at your preferred time control? Does the next challenge default to 10|0?

On custom games it does default back, I think. You could always just make sure that it's on the time control u want before playing...
Yes when I started a 5 0 custom game it remembered it next time.
Still I didn't do anything to cause this, so I presume chess.com did !
No scrub that. When I close the browser and come back a few minutes later its back defaulting to 10 minutes.
This needs to be fixed.

The last setting used to stick. You might open a ticket and see if that was a design decision or if a bug was introduced.
https://support.chess.com/customer/portal/emails/new

Btw are u actually staff? Cause I would like to be able to do many premoves at once on the chess.com app. The app only allows one premove at a time...making me almost always lose on time in one min. Could you report that to the staff?

No, just a moderator. You can post a suggestion in the Site Feedback & Suggestions forum or open a Suggestion ticket for that.
Well my rating had taken a dip anyway but I'm generally around 1280-1420 ish. Now its about 1130 cos I've aborted so many games. Its amazing hard to beat people at that level too

You just put in a ticket yesterday.
It can take a couple of days for a ticket to be looked at and if it is a bug it could take a little while to track down, fix, test and deploy. The developers are working on other bugs, fixes and updates so may not get to it immediately. It is also possible the change was intentional and won't be fixed, though I don't think that is the case.
I'm not saying that additional tickets can't be created, just that you should give them a little time to get to the ticket and work on the issue. If you created a ticket by the form, you should have received an automatic reply to it and it may be a day or two before you hear anything else.
I only play 1 minute 0 seconds, but this just happened to me when I went into Live. What's the deal? I don't want to play boring slow fuddy-duddy chess. The site remembered my preference up until today...