The Share Play connection was lost because the network connection became unstable.
To get the best experience from Share Play, both you and your friend will need a high-speed internet connection. The conditions surrounding the home network of each player may also impact internet connectivity. As a guide, a minimum connection speed of at least a 2Mbps is recommended. To check your upload speed, please check with your network service provider.
Hints for improving your network connection
• It is recommended that you use a LAN cable to connect your PS4 to the network.
• If you are using a Wi-Fi connection, place the PS4 and the router closer together, and make sure there are no obstructions between them.
• Other devices on your network might be using a large amount of bandwidth. Wait until they are finished.
• Check the connection status of the PS4 in [Settings] > [Network] > [Test Internet Connection].