i have xperia XA1 dual sim and it goes to silent mode automatically. i did fone restart it works for two or three days than after that it goes to silent mode automatically.
This can be an app acting up, I'd suggest that you perform a software repair using Xperia Companion. This will do a clean installation of the latest firmware and will also wipe your internal memory. Don't forget to backup using Xperia Companion, but preferably without adding apps or settings to the backup.
Follow the steps given in blue links, and keep us updated.
