Hey René,
I just checked, and the plugin is working correctly. My plugin only works on individual posts. This one, for example: https://dekloplossing.nl/7-tips-voor-een-onbezorgde-vakantie/ is working great. Here’s a screenshot:
https://s3-us-west-2.amazonaws.com/filestoobigtoemail/Screen+Shot+2015-01-06+at+11.28.45+AM.png
My plugin does not remove dates from home pages, or any archive pages (category, tag, etc). For that, I’d recommend modifying your theme files. The theme author may be willing to help with that.
The file you’d need to modify is located at themes/the-bootstrap/inc/template-tags.php
Never modify php files from within the WP dashboard (admin), always use a text editor and ftp or ssh.
Unfortunately, this extends outside of the realm of support I am able to provide for my plugin. I hope my tips have proved helpful.
Ben