Why, in Cubase 13, do assigned VST instruments from pre C13 projects show routed as "Side-Chain"

Can anyone explain to me this change in Cubase 13 where instrument routing used to show as seen in C11 below but now same project in C13 shows the instrument (in this case, Halion Sonic) shows under the new “Side-Chain” section?

If I add a new instance of Halion Sonic, or any other instrument, they go under “Windows MIDI” so why don’t the previously added ones go under “Windows MIDI”?
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