Disconnect with cause: "ExceptionOnConnect"

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Hi folks,

after a while, I built up a new version of my UWP app for Desktop x64 and I am encountering this issue:

as soon as I connect to Photon, I get disconnected with this DisconnectCause: ExceptionOnConnect.

In Unity editor everything is OK. With the previous version of the app everything is OK (same code for this part).

According to you, what the heck is going on?