It's interesting what you can find back in the stacks in libraries.
I agree with the writer that "Ol' Man River" sounds "under-rehearsed." Bix himself hits an uncustomary clam and seems to play over into a section and then stops, rather like the example on "Goose Pimples." It sounds like they were not altogether solid on the arrangement. A couple more run-throughs and another take or two might have produced a fine performance. Bix does finish strong on the final choruses.
I don't find Min Leibrook's solos on either song all that bad. Very few played anywhere near the quality of Rollini's solos and ensemble parts, it's true.