Issue originally reported here: https://www.mediawiki.org/wiki/Topic:Vhgb6y8dqm58yjni
When you open the same discussion page in two browser tabs, and try posting a new reply in each, MediaWiki does not detect the edit conflict (this is filed as T175745). DiscussionTools currently relies on edit conflict detection working correctly to handle that workflow. As a result, when saving the second reply, the first reply is lost (as if you reverted the previous edit).
Note that edit conflicts between different users are detected and automatically resolved (T240643). This problem only happens when the same user makes both edits.
This task is to figure out if we can fix the underlying MediaWiki bug, if we can get someone else to fix it (I've seen Phabricator activity of both WMDE and WMF Core Platform Team working on edit conflicts), or if we have to write our own edit conflict handling instead of relying on MediaWiki.