Opening the instance editor in one side and choosing the item at the other side has a near-guaranteed chance to cause Studio to error and close. The steps are:
- Open any place with Accurate Play Solo enabled.
- On either the server or the client, (it doesn’t matter which one you start at) find an object with a value set to an instance (like a Parent or an ObjectValue’s Value) and click the value to change it.
- Switch to the other side of the boundary and choose the object there from the explorer.
- Go back to the original location and after a few seconds, “An unexpected error occurred and Roblox needs to quit. We’re sorry!”
I found this on April 29, 2019. It seems mostly related to trying to set an instance value in the other side of where the start occurred, as sometimes it occurs without choosing the object.