Interesting. What’s your PWM frequency? If you have a 50Hz frequency then 1100-1900us pulses are likely too short to display with the LED (1.1 ms vs 1.9ms in every 20ms is 5.5% and 9.5% duty cycle respectively, which may not be enough to turn on the LED, and would likely be difficult to see a difference between regardless). If you had something like 200Hz then you get 22% vs 38% duty cycle which should be noticeable for your LED, and also easier to see on your oscilloscope
The width of the ‘on’ portion should be changing from 1.1 to 1.9ms (or 1100 to 1900us depending on the units of your scope). If that’s not happening then the PWM signal isn’t being updated.
Not sure how you’ve been testing on your scope, but try using cursors if you’re not already - if you trigger on the wave so you get stable pulses, then set two cursors to the on width for 1100us, then run the command on your Arduino to change to 1900us and you should see the cursors are now thinner than the on portion.