Images Not Showing Up

A friend asked me to troubleshoot his WordPress website: with the exception of the banner, none of his images are showing up.

I tried uploading them through the WordPress control panel, but any new images simply show up as a box with a generic image icon.

I’ve checked the file paths – they’re pointing to the right link. However, if I go directly to where the image file is stored, I simply get a 400 Bad Request error.

For example:
https://singinc.org/wp-content/uploads/%E6%9C%80%E7%BE%8E%E9%BA%97%E7%9A%84%E8%B7%AF.png
https://singinc.org/wp-content/uploads/水牛與蝴蝶.png

I’ve checked the image permissions: they’re on 755.

Anybody know what’s going on?

(Note: Coding amateur here, so layman’s terms would be greatly appreciated) ??