any changes in diet? caffeine, of course, has as significant impact on heart rate, ditto alcohol and a few other things. cold meds, immune response, etc. my heart rate jumps 10% a few days before i get the symptoms of a cold and also increases around that much from morning to afternoon as the catecholamines build up. stress and other adrenaline reactions do even more so. if i look at rides over a long period of time, the largest variation is what time of day the ride was. any chance you've started riding earlier? your 10 beats is only around 7 percent, well within the range that all those variations could produce.

anything more pathological than that .... certainly hard for us internet randoms to diagnose, and probably for a doctor as well without before and after testing of various types. the before will be hard to get at this point

the single greatest driver of the power : heart rate ratio for me over time has been left ventricular volume, which is seen and calculated with echocardiograms. if you had one done before and after, it would be interesting to know if there's a difference. ejection fraction will also factor in but it seems unlikely that your EF spontaneously went up unless you're recovering from disease or taking some serious meds.