That sounds like a small cookie issue with your browser, so you should try to login to play, mobile access via a fresh link to fix it. Just click here and try to enter your details again to refresh the session. Sometimes if the page was open for too long, the connection times out for security reasons. Once you refresh it, you should be able to open any slot without any problems. 7 Sinners is a great game by the way, I had a nice win on it just last night. The app version usually handles these sessions better because it does not rely on browser cookies. I find it much more stable for long gaming sessions where you switch between many different games. It is also a good idea to make sure your internet connection is stable. If it keeps happening, try a different browser like Chrome or Brave.