Strange, I've been using Componon's and Componon S's for quite a few years in various focal lengths and have never had a focus shift.

Someone on this forum had a very similar problem 6 months or a year ago, it turned out to be the enlarger head was creeping very slowly down the column. It was Durst enlarger in that case, they have a friction adjuster that wears over the years, you just need to tighten them every so often. I have had this happen myself but it showed up far more apparently.