Your Beoplay E8 3rd Gen remembers up to 8 Bluetooth pairings and only one device can be paired to the earphones at one time. When you pair the 9th device with your Beoplay E8 3rd Gen, it will automatically delete the profile of the first Bluetooth device that was paired.
When you want to switch between paired devices, disconnect from the currently paired device first before connecting it to another paired device.