Yes, I hooked up an oscilloscope to the signal and on the UNO I get 0.5ms to 2.5ms while on the D1 Mini Pro (esp8266) I get 1ms to 2ms. That explains a lot. Never knew that.
After googling this problem ad nauseam I found the "Servo - attach()" or might try `analogWriteFreq(new_frequency) to change the frequency from approximately 1Khz down to 500Hz, and see if that corrects the problem.
Thank you!