Ok, I see more people with this bug in FB and others forums groups, one day everybody will experiment this bug, I write my steps for "What to do when your game reset to level 1" in my experience.
(Update 26/02/19)
Before:
1. Always keep a screenshot of your Id Player and save in your device and cloud.
2. Take screenshots often about your game, currencies, storage....that things
3. Clear your cache often.
When the game save your progress:
1.Level up
2. New home style level
3. Make sims ( or retire sims and promote new ones)
4. Hosted parties
I am not pretty sure but apparently
5. Give stickers for the game force save your progress.
When happens:
1. Quickly soft reset your device as soon as you see the Create a Sim screen
2. Turn on your device
3. Clear cache
4. Open your game
This not testing by me, but you can tried, if not works you need contact with EA support it's the only way to have your progress back :/
***Please don't delete the app, this not solve this bug***
if you delete the app by mistake:
1. When the cloud option show you, please select from the cloud, even if says level 1 ( it's your old game, but level 1), these way the app install with the old id.
How to contact with EA
1. You can make the Initial Tutorial if you want to be sure your game it's already connect to Game Center or Google Play or you dont know your id Player, probably you can see your friends, so it's your same game with new Level 1, it's not necessary do the tutorial if your not want.
2. Open the tab of Help from the panel of control and request help direct from the app and make a case, also if you don't do the tutorial you can make a case from EA Help page web.
2.1 When your open a new case select, technical issues>lost progress
2.2 The EA people manage a lot of games, so they really don't know sometimes what to do, so you need tell them what to do, you can write something like this:
"Hi, I was play normal (date and hour) with my game and today ( date and hour) start as a new one from the beginning tutorial, my game it's already connect with my Game Center, FB and EA accounts, so it's not a cloud problem, I do the basics steps for ios Problems but dont work.
Can you please roll back my progress in the most recently date your has save in your server??
I know some players get back their progress, when ask for help and EA rolled back their progress a date before they happens
I attach a image of my id player and my game before of my game reset ( attach a image of your id and one of your game, maybe a imagen of your new game level 1).
Thanks"
For fast Help:
3. if in your Country it's available the phone calls better make a phone call with your number of case.
3.1 You can request Help from EA Help FB page with your number of case, ( if you not make a case, they will request you make a new one)
4. Some agents will tell you, you need to do the tutorial and download your game from the cloud, so explaint IT'S ALREADY CONNECTED, and it's a bug, please don't delete the app.
4.1 Some agents will tell you, your lost your account, you better close the case and open a new one or contact with other people.
5. ALWAYS request a roll back your progress.
When EA roll back your progress
1. Force close the app in all your devices and not play, it's very important force close the app when EA roll back your game or can fail.
some EA people can say "log out" its means force close the app, not log out from Game Center or Google Play
2. When EA roll back your game, means you will lose progress if you have luck could be a day or two, but sometimes this a month or more.
Always EA roll back your account in your last hosted party in the most of cases.
3. Take a screenshots of your purchases and EA give you purchases back, sometimes you need a new case only for this.
Theories:
1. Force close the app a lot can make your game more glitched
2. The days when it's more common to have this bug:
Mondays and Wednesdays when the stickers and host parties resets, when the stickers contest reset in the middle of week and a new update this near.
if somebody have more suggestions can comment