I can't say that this comment is particularly useful, both with the issue you described or with the recommendation to find another brand.
You purchase a paper backed adhesive sheet, and let it sit for months had less than satisfactory results. You neglected to mention how you stored them, or what in kind of environment, during the months without use. You also did not mention how to attempted to remove the film, or if this happened with a single or multiple sheets.
And when it comes to the brand you recommend finding a reputable one; Fellowes is almost as well known as Avery, and both are considered reputable mid grade companies. Do you have a specific alternative you can recommend, or are you just frustrated and looking for a place to vent?