If the language of the operating system differs from the English Illustrator installation there may be problems. I use another OS language than english, and use COMMAS “,” instead of DOTS “.” when I write numbers.
Illustrator some way or another can’t parse the 0.25 or 0.50 when I choose it with the cursor or scroll through the numbers with my keystrokes. I have to type the stroke weight with COMMAS not DOTS.
Example:
If I want to get 0.5 thickness. Do get it to work I have to type in “0,50” not “0.50”