Hello Moritz, thank you for appreciating my work.
The bug you are describing is weird, it could be related to a filesystem issue (reading or writing rights or something like that) or a security issue (e.g. the webpage is served as https while the images are served as http).
What can you do?
1. Check your browser console for errors
Are there errors in the browser console?
2. Verify that the plugin created all needed files on first activation
If you can browse your site filesystem please check inside \wp-content\uploads\da-reactions
This folder should contain, among other things, all reaction images used in your site, by default there are 6 images in SVG format:
All files follow this naming convention:
If those images are missing or corrupted you may delete all of them, the plugin will retry to create images the next time you deactivate and reactivate the plugin.
Please let me know if deleting and reactivating the plugin works, if not please send me the complete configuration of your site (WordPress version, Theme name and version, all Plugins names and versions) and I will try to reproduce the bug on my machines.
Thank you for asking.