Think the device can deliver the 1mA, because I can measure 5V-level on the input of the voltage devider.
But I think, that the WEMOS D1 has a somehow internal resistor, that is parallel to the 3,3k and makes him to ~450R.
Then Ohms law will be correct again....
Just ordered some 3,3V Z-diodes. Try to place them instead of the 3,3k resistor and make the 1,8k bigger to ~10k.