There is something explicitly hiding comments, either a theme/plugin you use OR one of your CSS snippets if any. I tested in my vault and comments appear just fine.
You can clearly see that the line number 9 in the above screenshot is overlapped with line number 10, so something is turning comments invisible via CSS.
You can try disabling CSS snippets one by one, then try changing the theme to the default Obsidian theme, and then try disabling plugins one by one.