ConverseJS bundle a library called bootstrap.native. TikiWiki also uses the same library to show dropdows, buttons and modal forms. The problem is this library is loaded twice and causes a lot of conflicts and strange behaviors in Tiki interface.
There is no easy workaround to this problem. Actually, a patch was written to completely remove bootstrap.native from ConverseJS and force to use the bootstrap.native loaded by Tiki. This patch should be updated whenever ConverseJS is updated, otherwise it will not be applied by composer correctly.
The patch file, as of Tiki 20.x, is located at
1. Install the ConverseJS using the composer tool
composer require -d vendor_bundled npm-asset/converse.js:5.0.5 --ignore-platform-reqs
2. Manually create a patch to remove bootstrap.native from ConverseJS
3. Check every place in conversejs.css where resource are loaded from /dist/ and override it in lib/xmpp/css/conversejs.css