Emojis replaced by '?' automatically

I just discovered that all emojis on my site were replaced by the ? char. I saw this on comments and posts.

Tables like wp_comments or wp_posts had a utf8mb4_unicode_ci collation before and now, so that is not the issue.

I'm thinking on WP core or a plugin update causing this. Also, I faced an odd issue where some post updates I made disappeared, so it might be possible that my shared hosting has been messing around with my DB.

Have you seen this issue before? How can I know which was the root cause?