Some characters, primary punctuation, do not support variable font weights which also impacts the predefined font weights.
This is a list of all the characters in hex that i could identify:
21,21,27,28,29,2C,3A,3B,3F,5B,5D,7B,7D,A1,B7,BF,F7,13F,13f/c2sc,140,140/smcp,2018,2019,201A,201B,201C,201D,201E,2022,2024,2025,2026,2032,2033,203C,203D,2219
This can also be seen/tested with a tool like https://wakamaifondue.com settings the font-weight to the minimum or using the light font style