Qlik Sense is using jquery 3.0 and there is a known compatibility issue between bootstrap 4 and jquery 3 =>
Maybe that's the issue
I hope this helps
I came across this some time ago, with an earlier version of Bootstrap 4. The problem is that Bootstrap 4 needs a newer version of jQuery, and the jQuery that is bundled with Qlik Sense (actully in the requirejs file) overwrites that one.
I don't know if my solution is the best, there might be a more elegant one, but I did like this, basically saving the Bootstrap4 jQuery instance before loading the qlik version, and then restoring it:<script src="node_modules/jquery/dist/jquery.slim.min.js"></script>
window.jQueryB = window.jQuery;
window.$ = window.jQuery = window.jQueryB;
Hope this helps