Simplified Chinese: Mismatched Line Weight Mystery

I've got a Rise course in Chinese (simplified) and there are some sections where I can see characters that don't share the same line weight as the characters they're next to. They are bold, but not as bold as their neighbors. This, despite the fact that in other Rise course with the same Theme, I can see the character matching the line weight of its neighbors.

Here's a screenshot where I found a "skinny" character on the left in my current project, and on the right a version in another project where the line weight matches the rest of the line. (It's the same character highlighted in yellow, bold in both settings.)

Same fonts (Raleway) and the old, correct version doesn't turn skinny when I match the font size either. There's something unique about the new formatting that I can't figure out.

I tried uploading custom fonts as recommended, but that introduced other problems, so... any ideas how I figure out why some of these characters aren't matching their neighbors with regards to stroke width?