Hi @Hdicu,

• Does the reply actually get posted? (What do you see in the page history?)
• Is the wiki on which you’re experiencing this problem publicly available? If yes, can you post its URL? It’s easier to debug if one can actually see the bug.
• Do you get any JavaScript errors?
• What do you see in the URL bar after posting the reply? DiscussionTools often changes URLs after posting; while I don’t think this is the culprit, this piece of information may help debugging.
• Does this affect the new topic tool as well, or only the reply tool?

The URL after replying was https://minecraft.wiki/w/Minecraft_Wiki_talk:Community_portal?curid=2925&diff=0#I_have_a_very_very_bad_problem.
There was following error in DevTools after posting it:

Thanks for the details! Is this the only error you get? I tried to understand how the code works a Wikimedia wiki (because I posted a comment there anyway, so I don’t clutter the page history; but as far as I see, this part of the code hasn’t changed substantially in the past year, so it should be good enough for a general understanding), and I noticed that by the time the code indicated in the error message runs, the reply should have already appeared. So I think this is a secondary problem caused by an earlier error.

I forgot to ask last time: does the bug also appear in safe mode (docs)? If not, it’s likely caused by a site script, user script or gadget interfering with DiscussionTools.

Which exact version and branch of the DiscussionTools extension is installed?

Does that mean that you are mixing MediaWiki 1.43 code with the git master code of extensions?

I don't know. The wiki is hosted by Weird Gloop, not me.

It’s https://github.com/weirdgloop/mediawiki-extensions-DiscussionTools/commit/5fbd9c2ffbfecae352a567b1b9859de76df891b0. While now we know what code version is being run, it’s a fork (and a fork of master), so there’s indeed no compatibility guarantee. You should contact Weird Gloop as the maintainers of the version they run. (I couldn’t find out why they forked it apart from this generic descreption on their meta wiki.)