I haven't heard of this.
My kidney function isn't great - eGFR around 55 ever since my first ever blood test years before prostate cancer, but it hasn't ever got any worse, so no one has been concerned about it. Strangely, it increased to 60 while I was on Bicalutamide, but that's just about within the noise variation, so probably not significant.
This particular blood test is screwed up by either doing exercise in the previous 24h or eating lots of protein (maybe only animal protein?), both of which bump up your creatinine level, from which the eGFR is calculated. This is because stressing your own muscles results in creatinine breakdown products, and eating muscle similarly releases lots of creatinine as you digest it.