I have a reply from AurallySound who also say panning can be an issue and Take Five is panned strongly:
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I took a listen and expected it to do considerably better than it did. My guess would be the rather unusual panning of instruments (the center is really open (!)) is quite different from the rock/pop songs used to train the stem separator. Will training does do some dynamic re-panning it doesn't do anything as extreme as pushing the drums so far left--perhaps something to look into.
Take Five was recorded in 1959, so could have originally been mono limited stereo. That they expected it to do better is encouraging, though some other tunes I tried were also less than brilliant.

Jazz relative beginner, starting at a much older age than was helpful.
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