Passing osascript via .Net CORE gets syntax error: A unknown token can't go here
WORK AROUND:
I solved the issue by putting the above in an Applescript and calling the script from C#. Meant having to add a non .Net file to the project which can only be edited on a Mac (so far as I know). Script is:

on run argv
    tell application "terminal"
        activate
        do script ("idevicesyslog -u " &amp; item of argv &amp; " | tee '" &amp; item 2 of argv &amp; "'")
    end tell
end run


The script was called by using System.Diagnostics.Process and passing in osascript.exe and the two arguments into the ProcessStartInfo constructor.