NE555 above 100kHz frequency problem
The Texas Instruments "NE555" recommended R values are  1k ohms and more,
and 1 MHz operation of that part is not guaranteed.   100kHz is the recommendation.   NE555 datasheet

More modern variant designs can handle 1 MHz easily, including (again, from Texas Instruments) TLC555 TLC555 datasheet
and THAT datasheet explicitly notes discharge internal resistance (about 20 ohms) meaning that R1 and R2 ought to be much higher (4k ohms would be good).