No 120 backing paper problems for me ever, past-date frozen or not. I do of course rotate my inventory, and use up older film first. But high speed films are inherently subject to faster emulsion aging due to cosmic rays, and so don't store well long-term even frozen.
There is a parallel thread over on Photrio right now, surmising the proprietary trade secret nature of Kodak's current backing paper. And yes, it does feel more slippery or "plasticky". What Ilford happens to be using is a slightly different question.
Sheet film, fortunately, is immune from such issues.
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