i had a colleague look into it aswell, this is what he wrote

I was able to reproduce the error on your wiki. This error is internal to D=
iscussionTools. I've looked into whether or not the error was caused by a m=
isconfiguration of the extension, but it is not, nor can I find evidence to=
suggest that it has anything to do with the setup of the wiki at all.

There's clearly an error in the extension, but I've read through the nginx =
error logs as well as the MediaWiki debug log, but neither of those gave an=
y indication what the error actually is.

Therefore:

• configuration is correct
• multi-database structure is not a problem
• no error is logged in the nginx logs
• no error is logged in the mediawiki debug log

Since this is an older version of MediaWiki (1.39.x) I would first check that the version of DiscussionTools properly corresponds to the version of MediaWiki you are using. Version skew between Parsoid (which should be bundled with core) and the DiscussionTools extension would be a good explanation of errors of this sort.

i just checked on Special:Version, apparently this is the Version I have installed:

Version 0.0.0 (b03f139) 08:08, 5. Sep. 2023

That seems correct.

cananian:~/Wikimedia/Extensions/DiscussionTools$ git log origin/REL1_39
commit 2d87dd9f54a9a0974a7b2750a90e13aa49ccbc6f (origin/REL1_39)
Author: Translation updater bot <l10n-bot@translatewiki.net>
Date:   Tue Sep 12 07:51:44 2023 +0200

    Localisation updates from https://translatewiki.net.
    
    Change-Id: I321dcfa47a161f3a5e6b80fe1c8b5428f7775dae

commit b03f1394ce634c31418703bb8f46fd00807e5fe2
Author: Translation updater bot <l10n-bot@translatewiki.net>
Date:   Tue Sep 5 08:08:29 2023 +0200

    Localisation updates from https://translatewiki.net.
    
    Change-Id: I628c6bfd0e440a7de1cf43dd4cbe19c100b1b46b

@Ibo2910 I don’t know how important F37721430 is, but please be aware that no one except for you sees it (cf. https://www.mediawiki.org/wiki/Phabricator/Help#File_visibility).

Thanks, now I can see it.

Is there any more Information that i could give you?

In T345932#9167290, @cscott wrote:

That seems correct.

cananian:~/Wikimedia/Extensions/DiscussionTools$ git log origin/REL1_39
commit 2d87dd9f54a9a0974a7b2750a90e13aa49ccbc6f (origin/REL1_39)
Author: Translation updater bot <l10n-bot@translatewiki.net>
Date:   Tue Sep 12 07:51:44 2023 +0200

    Localisation updates from https://translatewiki.net.
    
    Change-Id: I321dcfa47a161f3a5e6b80fe1c8b5428f7775dae

commit b03f1394ce634c31418703bb8f46fd00807e5fe2
Author: Translation updater bot <l10n-bot@translatewiki.net>
Date:   Tue Sep 5 08:08:29 2023 +0200

    Localisation updates from https://translatewiki.net.
    
    Change-Id: I628c6bfd0e440a7de1cf43dd4cbe19c100b1b46b

is there anything else i could check?

I've look into this a little bit..
The CommentController.prototype.startPoll = function () in /modules/CommentController.js starts polling for me as soon as I click on the reply button at a comment.
The click starts the first api call : GET /api.php?action=discussiontoolscompare&format=json&formatversion=2&uselang=de&fromrev=1372&totitle=Test, but it is a red url and gets no response at all, thus the pop-up comes "Could not find the comment..".
the polls done after, are the exact same calls: GET /api.php?action=discussiontoolscompare&format=json&formatversion=2&uselang=de&fromrev=1372&totitle=Test, but now they do work.
If you look at the screenshot, the red calls are my mouseclick. The others are just polled in the background the whole time.
Anyone any ideas? Cors settings etc are all set properly.

The errors look like as if the loading was blocked by a Firefox extension or the privacy settings of Firefox. Did you try disabling any extensions you have? You could also try disabling the Firefox tracking protection by clicking on the shield icon in the URL bar, although I don’t think that would selectively block some requests while letting others go through.

In T345932#9307038, @Tacsipacsi wrote:

The errors look like as if the loading was blocked by a Firefox extension or the privacy settings of Firefox. Did you try disabling any extensions you have? You could also try disabling the Firefox tracking protection by clicking on the shield icon in the URL bar, although I don’t think that would selectively block some requests while letting others go through.

The screenshot is from FireFox, but this is the case for Chrome and Safari as well. Both Chrome and Safari are only used for testing and have no extensions installed.

You mean that you get the same (or very similar) error in Chrome and Safari as well, or just that they’re also broken (but you didn’t try or wasn’t able to pinpoint suspicious log entries)?

In T345932#9312096, @Tacsipacsi wrote:

You mean that you get the same (or very similar) error in Chrome and Safari as well, or just that they’re also broken (but you didn’t try or wasn’t able to pinpoint suspicious log entries)?

Ah sorry, I do not get any notifications or emails for some reason, so I did not notice your post yet.
Similar message where it cannot retrieve the url.

is there more i could check?

@Sen-Sai @Ibo2910 Do either of you have a custom $wgArticlePath, i.e. /$1/ instead of /wiki/$1/? If so, T346735: Reply tool doesn't show when the wiki not run on subFolder like /wiki/ may be your issue. On my end, I get the same kind of errors as T345932#9304485 on my wiki which has a $wgArticlePath of /$1/.