Regardless of old wive's tales, higher octane does not mean higher performance! Remember that, higher octane does not mean higher performance. All octane does is stop pinging, as in autoignition that higher compressions can cause by igniting the gas from compressing the mixture to much, rather like diesels are supposed to do. The stuff you have to put in the gas, formerly tetraethyl lead, I don't know what kinda crap they use nowadays, but whatever they put in there takes away the power from the gas. Drag racers in the know only add as much antiknock material to keep the knocking down, but the octane remains as low as they can get away with because low octane fuel provides more energy. There is no reason at all to use higher octane in a stock Royal Enfield.
Go back to the stuff that was working. You didn't mention what brand of gas you were using, but because it all contains different ingredients, there are varying qualities out there.
I have no recommendations. I usually use 76 because it is available close to the house. The bikes ran fine.
Bare