I don't know anything about the issue, but would suspect a manufacturing difficulty if it's been that long. You might try giving them a shoutout on their contact form.
Consider buying the equivalent in Rosco. It still requires a double gel holder as the heat shield and the color gel must have some physical seteration.
And as FWIW, I never found that the so-called Lee Hi-Temp outlasted the regular Lee or any of the Rosco, Apollo or GAM products. My take was it was a gimmick to copy a lot of the more popular Roscoline and that they needed a new name. Thus often times, if there's a matching Rosco version, I use that.
Late reply, but I have to disagree wit ST, as i have found, especially in older 360Q's that the HT colors do seem to last a bit longer. Your mileage may bary.