Thanks for the information @Zdepam I also think there must be some setting that is blocking the connection, but I am unfamiliar with the device so can't really speak to specifics. I would suggest you check to make sure you have given the proper permissions to SBI in Facebook, too, in case an update changed it somewhere.
Have you filed a support request SimCity BuildIt Support request? I would suggest you link this thread in your request, and be sure to include the details about your phone, including the OS version.
Edit: I did find a couple of reports on the Samsung website that sound similar. No real solutions, other than overloaded servers. Which might actually be the real reason, but it does seem odd that it's connected to this particular model. https://us.community.samsung.com/t5/Other-Mobile-Devices/Wifi-issue-Galaxy-A71/td-p/1147590 https://us.community.samsung.com/t5/Gamer/disconnection-while-playing-games/m-p/1179396
Are you connecting from the US, or another country?