A rare bug in macOS' Screen Sharing service may result in the following symptoms:
- Before disconnecting a Screens session, mouse and keyboard input to the remote Mac may fail.
- Curtain Mode remains active on the remote Mac after disconnecting a Screens connection.
- Attempting subsequent connections to the remote computer results in a "Connection cancelled" message. Apple is aware of and has acknowledged this issue, but no resolution has been offered as of yet. The Mac user community, however, has offered a few work-arounds you may try.
Source: https://support.apple.com/HT203251