You might experience that your Xperia Dual SIM device restarts when switching between SIM1 and SIM2. This happens on some devices when you have two SIM cards that need different configurations.
The active configuration is chosen based on the SIM card being used. Among the configuration items are the modem parameters, that make sure the connection works well with the current SIM. The parameters require a restart for changes to take effect. When the data connection is moved to a SIM card requiring different settings, the device restarts to change them.