CJK Font Shader Box

Hi, im facing an issue duing using japanese fonts in unity. The cjk fonts got box shader if the text was small size. Here is the picture of that issue. Any other facing the same issue? Please help me if any of pro unity developer got any answer for this issue. Thank you!
image

EDIT: Im using textmeshpro and create an asset with multiple fallbacks based on the amount of CJK symbols needed. Somehow Im getting this box like shade but it sometimes doesnt show when the font is big enough