Joining a session in PIE with Auto Connect To Server disabled will crash PIE.
Note: this is not specific to the Multiplayer Shootout project used in the repro steps; this will occur in any project with a simple Create/Find/Join session approach to connection.
Reproduced in 4.9.2 binary, 4.10 binary, and Main (CL# 2761843). The Auto Connect To Server toggle was not available in earlier versions.
1. Open the Multiplayer Shootout project
2. Editor Preferences > Play > Multiplayer Options, disable Auto Connect To Server
3. PIE with 2 players
4. In one PIE window, click Play
5. In the other PIE window, click Find Games
6. Click the available session when it appears in the list
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