My Lgv Challenger Ultra has changed its diet

I have had the pleasure of owning this rifle for several years since new. No work has been done on it. Over the last week or so I noticed that it was waning in the accuracy department.
I started using Ftt 14.66 gr in 5.53 head size when first purchased and I was very happy with the accuracy, but about 2 years ago the 14.66 gr pellets started not group as well. I did all the usual things when accuracy starts to wane but I couldn’t get it to group as well as previously. I had been using FTT Green 9.56 gr on one of my other rifles so in desperation I tried the Greens. The transformation was instantaneous she was back to her best if not more better than before. This went great for several months, these light pellets really zipped and I was using less holdover and in fact it was like shooting a 177 cal. But like everything else this changed and I was back to accuracy problems.
So back to the 14.66 gr lead pellets and all was good again however there was a noticeable difference in group sizes between the lead and Green pellets.
Leap forward to yesterday and today. Again the groups started to open up. I have been shooting the H&N Baracuda 12.65 gr Greens with great success in my Hw50S since new and I thought id give them a try. Accuracy is back on par with the lighter Ftt Greens so for the moment I’m happy.
Has anybody else had these issues with their rifle going “ off “ it’s usual feed?
Gary