how to get unsaved traces?

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Most likely you can't retrieve any old unsaved capture files, but you can try looking in your temp folder; sometimes old capture files linger there if not cleaned up properly.

Run tshark -G folders | grep "Temp" to find the location of your temp folder, unless you're on Windows then run "C:\Program Files\Wireshark\tshark.exe" -G folders | findstr "Temp".