==== Error ====
* mwversion: `1.37.0-wmf.18`
* reqId: `349d7f26-fb29-401e-b010-830b487e6c9b`
* [[ https://logstash.wikimedia.org/app/dashboards#/view/AXFV7JE83bOlOASGccsT?_g=(time:(from:'2021-08-11T20:10:45.000Z',to:'2021-08-12T20:14:34.286Z'))&_a=(query:(query_string:(query:'reqId:%22349d7f26-fb29-401e-b010-830b487e6c9b%22'))) | Find reqId in Logstash ]]
* [[ https://logstash.wikimedia.org/app/dashboards#/view/AXFV7JE83bOlOASGccsT?_g=(time:(from:now-30d,to:now))&_a=(query:(query_string:(query:'normalized_message:%22%5B%7BreqId%7D%5D%20%7Bexception_url%7D%20%20%20Wikimedia%5CAssert%5CInvariantException:%20Invariant%20failed:%20Comments%20are%20always%20preceded%20by%20headings%22'))) | Find normalized_message in Logstash ]]
```name=normalized_message
[{reqId}] {exception_url} Wikimedia\Assert\InvariantException: Invariant failed: Comments are always preceded by headings
```
```name=exception.trace,lines=10
from /srv/mediawiki/php-1.37.0-wmf.18/vendor/wikimedia/assert/src/Assert.php(224)
#0 /srv/mediawiki/php-1.37.0-wmf.18/extensions/DiscussionTools/includes/Notifications/EventDispatcher.php(119): Wikimedia\Assert\Assert::invariant(boolean, string)
#1 /srv/mediawiki/php-1.37.0-wmf.18/extensions/DiscussionTools/includes/Notifications/EventDispatcher.php(144): MediaWiki\Extension\DiscussionTools\Notifications\EventDispatcher::groupCommentsByThreadAndName(array)
#2 /srv/mediawiki/php-1.37.0-wmf.18/extensions/DiscussionTools/includes/Notifications/EventDispatcher.php(102): MediaWiki\Extension\DiscussionTools\Notifications\EventDispatcher::generateEventsFromParsers(array, MediaWiki\Extension\DiscussionTools\CommentParser, MediaWiki\Extension\DiscussionTools\CommentParser, MediaWiki\Revision\RevisionStoreRecord, Title, User)
#3 /srv/mediawiki/php-1.37.0-wmf.18/extensions/DiscussionTools/includes/Hooks/EchoHooks.php(91): MediaWiki\Extension\DiscussionTools\Notifications\EventDispatcher::generateEventsForRevision(array, MediaWiki\Revision\RevisionStoreRecord)
#4 /srv/mediawiki/php-1.37.0-wmf.18/includes/HookContainer/HookContainer.php(338): MediaWiki\Extension\DiscussionTools\Hooks\EchoHooks::onEchoGetEventsForRevision(array, MediaWiki\Revision\RevisionStoreRecord, boolean)
#5 /srv/mediawiki/php-1.37.0-wmf.18/includes/HookContainer/HookContainer.php(137): MediaWiki\HookContainer\HookContainer->callLegacyHook(string, array, array, array)
#6 /srv/mediawiki/php-1.37.0-wmf.18/includes/Hooks.php(137): MediaWiki\HookContainer\HookContainer->run(string, array, array)
#7 /srv/mediawiki/php-1.37.0-wmf.18/extensions/Echo/includes/DiscussionParser.php(165): Hooks::run(string, array)
#8 /srv/mediawiki/php-1.37.0-wmf.18/extensions/Echo/includes/EchoHooks.php(494): EchoDiscussionParser::generateEventsForRevision(MediaWiki\Revision\RevisionStoreRecord, boolean)
#9 /srv/mediawiki/php-1.37.0-wmf.18/includes/deferred/MWCallableUpdate.php(38): EchoHooks::{closure}()
#10 /srv/mediawiki/php-1.37.0-wmf.18/includes/deferred/DeferredUpdates.php(515): MWCallableUpdate->doUpdate()
#11 /srv/mediawiki/php-1.37.0-wmf.18/includes/deferred/DeferredUpdates.php(391): DeferredUpdates::attemptUpdate(MWCallableUpdate, Wikimedia\Rdbms\LBFactoryMulti)
#12 /srv/mediawiki/php-1.37.0-wmf.18/includes/deferred/DeferredUpdates.php(221): DeferredUpdates::run(MWCallableUpdate, Wikimedia\Rdbms\LBFactoryMulti, Monolog\Logger, BufferingStatsdDataFactory, string)
#13 /srv/mediawiki/php-1.37.0-wmf.18/includes/deferred/DeferredUpdatesScope.php(267): DeferredUpdates::{closure}(MWCallableUpdate, integer)
#14 /srv/mediawiki/php-1.37.0-wmf.18/includes/deferred/DeferredUpdatesScope.php(196): DeferredUpdatesScope->processStageQueue(integer, integer, Closure)
#15 /srv/mediawiki/php-1.37.0-wmf.18/includes/deferred/DeferredUpdates.php(242): DeferredUpdatesScope->processUpdates(integer, Closure)
#16 /srv/mediawiki/php-1.37.0-wmf.18/includes/MediaWiki.php(1136): DeferredUpdates::doUpdates(string)
#17 /srv/mediawiki/php-1.37.0-wmf.18/includes/MediaWiki.php(846): MediaWiki->restInPeace()
#18 /srv/mediawiki/php-1.37.0-wmf.18/includes/MediaWiki.php(584): MediaWiki->doPostOutputShutdown()
#19 /srv/mediawiki/php-1.37.0-wmf.18/index.php(53): MediaWiki->run()
#20 /srv/mediawiki/php-1.37.0-wmf.18/index.php(46): wfIndexMain()
#21 /srv/mediawiki/w/index.php(3): require(string)
#22 {main}
```
==== Impact ====
logspam.
==== Notes ====
Not sure if there is visible breakage but there is quite a lot of logspam from this.