Steps to reproduce:
1. Open ,,Freeze repro"
2. Press Play and after few seconds exit the Play mode
3. Open ,,script" which is located in the Assets folder
4. Edit a script in any way (pressing space in an empty line is enough) and save it
5. Go back to scene view
6. Select any GameObject and switch between GameObjects in the scene until Unity freezes

Expected results: Unity works without any problems
Actual results: Unity freezes to the point that sometimes it needs to be shut down with a task manager

Reproducible with: 2017.4.16f1, 2018.2.18f1, 2018.3.0b12, 2019.1.0a11

Note: PhotonNetwork.ConnectUsingSettings() has to be used in public override void OnDisconnected(DisconnectCause cause) function. Also, the freeze will appear when any script in the scene is edited as long as there is a GameObject with a script in the scene