Looks like we hit the exception added in rELQTa91f43c89443: Add an exception to synchroniseArticleData when called on a null article, so…
I didn't see anything in WMF Logstash nor any suspicious recent changes in LQT itself. Maybe not recently introduced error.
[2019-10-31 04:18:35] error.WARNING: [aa9df05a8c6ccf5e2e4aca5a] /w/api.php?action=feedthreads&type=replies%7Cnewthreads&thread=Thread%3AUser+talk%3A%E1%83%9B%E1%83%90%E1%83%A0%E1%83%92%E1%83%90%E1%83%9A%E1%83%9D%E1%83%9C%E1%83%90%2FTranslation+request+for+Georgian&feedformat=atom ErrorException from line 593 of /srv/mediawiki/tags/2019-10-30_14:28:46/extensions/LiquidThreads/classes/Thread.php: PHP Notice: Exception doing lazy updates: Exception: synchroniseArticleData called on null article in /srv/mediawiki/tags/2019-10-30_14:28:46/extensions/LiquidThreads/classes/Threads.php:308 Stack trace: #0 /srv/mediawiki/tags/2019-10-30_14:28:46/extensions/LiquidThreads/classes/Thread.php(968): Threads::synchroniseArticleData(NULL, 100, 'cascade') #1 /srv/mediawiki/tags/2019-10-30_14:28:46/extensions/LiquidThreads/classes/Thread.php(591): Thread->doLazyUpdates() #2 /srv/mediawiki/tags/2019-10-30_14:28:46/extensions/LiquidThreads/classes/Thread.php(519): Thread->__construct(Object(stdClass)) #3 /srv/mediawiki/tags/2019-10-30_14:28:46/extensions/LiquidThreads/classes/Thread.php(729): Thread::newFromRow(Object(stdClass)) #4 /srv/mediawiki/tags/2019-10-30_14:28:46/extensions/LiquidThreads/classes/Threads.php(97): Thread::bulkLoad(Array) #5 /srv/mediawiki/tags/2019-10-30_14:28:46/extensions/LiquidThreads/classes/Threads.php(104): Threads::loadFromResult(Object(Wikimedia\Rdbms\ResultWrapper), Object(Wikimedia\Rdbms\MaintainableDBConnRef), true) #6 /srv/mediawiki/tags/2019-10-30_14:28:46/extensions/LiquidThreads/classes/Threads.php(157): Threads::where(Array, Array, true) #7 /srv/mediawiki/tags/2019-10-30_14:28:46/extensions/LiquidThreads/api/ApiFeedLQTThreads.php(187): Threads::withRoot(Object(Article)) #8 /srv/mediawiki/tags/2019-10-30_14:28:46/extensions/LiquidThreads/api/ApiFeedLQTThreads.php(58): ApiFeedLQTThreads->getConditions(Array, Object(Wikimedia\Rdbms\MaintainableDBConnRef)) #9 /srv/mediawiki/tags/2019-10-30_14:28:46/includes/api/ApiMain.php(1603): ApiFeedLQTThreads->execute() #10 /srv/mediawiki/tags/2019-10-30_14:28:46/includes/api/ApiMain.php(539): ApiMain->executeAction() #11 /srv/mediawiki/tags/2019-10-30_14:28:46/includes/api/ApiMain.php(510): ApiMain->executeActionWithErrorHandling() #12 /srv/mediawiki/tags/2019-10-30_14:28:46/api.php(83): ApiMain->execute() #13 {main} {"exception":"[object] (ErrorException(code: 0): PHP Notice: Exception doing lazy updates: Exception: synchroniseArticleData called on null article in /srv/mediawiki/tags/2019-10-30_14:28:46/extensions/LiquidThreads/classes/Threads.php:308 Stack trace: #0 /srv/mediawiki/tags/2019-10-30_14:28:46/extensions/LiquidThreads/classes/Thread.php(968): Threads::synchroniseArticleData(NULL, 100, 'cascade') #1 /srv/mediawiki/tags/2019-10-30_14:28:46/extensions/LiquidThreads/classes/Thread.php(591): Thread->doLazyUpdates() #2 /srv/mediawiki/tags/2019-10-30_14:28:46/extensions/LiquidThreads/classes/Thread.php(519): Thread->__construct(Object(stdClass)) #3 /srv/mediawiki/tags/2019-10-30_14:28:46/extensions/LiquidThreads/classes/Thread.php(729): Thread::newFromRow(Object(stdClass)) #4 /srv/mediawiki/tags/2019-10-30_14:28:46/extensions/LiquidThreads/classes/Threads.php(97): Thread::bulkLoad(Array) #5 /srv/mediawiki/tags/2019-10-30_14:28:46/extensions/LiquidThreads/classes/Threads.php(104): Threads::loadFromResult(Object(Wikimedia\\Rdbms\\ResultWrapper), Object(Wikimedia\\Rdbms\\MaintainableDBConnRef), true) #6 /srv/mediawiki/tags/2019-10-30_14:28:46/extensions/LiquidThreads/classes/Threads.php(157): Threads::where(Array, Array, true) #7 /srv/mediawiki/tags/2019-10-30_14:28:46/extensions/LiquidThreads/api/ApiFeedLQTThreads.php(187): Threads::withRoot(Object(Article)) #8 /srv/mediawiki/tags/2019-10-30_14:28:46/extensions/LiquidThreads/api/ApiFeedLQTThreads.php(58): ApiFeedLQTThreads->getConditions(Array, Object(Wikimedia\\Rdbms\\MaintainableDBConnRef)) #9 /srv/mediawiki/tags/2019-10-30_14:28:46/includes/api/ApiMain.php(1603): ApiFeedLQTThreads->execute() #10 /srv/mediawiki/tags/2019-10-30_14:28:46/includes/api/ApiMain.php(539): ApiMain->executeAction() #11 /srv/mediawiki/tags/2019-10-30_14:28:46/includes/api/ApiMain.php(510): ApiMain->executeActionWithErrorHandling() #12 /srv/mediawiki/tags/2019-10-30_14:28:46/api.php(83): ApiMain->execute() #13 {main} at /srv/mediawiki/tags/2019-10-30_14:28:46/extensions/LiquidThreads/classes/Thread.php:593) [stacktrace] #0 [internal function]: MWExceptionHandler::handleError(1024, 'Exception doing...', '/srv/mediawiki/...', 593, Array) #1 /srv/mediawiki/tags/2019-10-30_14:28:46/extensions/LiquidThreads/classes/Thread.php(593): trigger_error('Exception doing...') #2 /srv/mediawiki/tags/2019-10-30_14:28:46/extensions/LiquidThreads/classes/Thread.php(519): Thread->__construct(Object(stdClass)) #3 /srv/mediawiki/tags/2019-10-30_14:28:46/extensions/LiquidThreads/classes/Thread.php(729): Thread::newFromRow(Object(stdClass)) #4 /srv/mediawiki/tags/2019-10-30_14:28:46/extensions/LiquidThreads/classes/Threads.php(97): Thread::bulkLoad(Array) #5 /srv/mediawiki/tags/2019-10-30_14:28:46/extensions/LiquidThreads/classes/Threads.php(104): Threads::loadFromResult(Object(Wikimedia\\Rdbms\\ResultWrapper), Object(Wikimedia\\Rdbms\\MaintainableDBConnRef), true) #6 /srv/mediawiki/tags/2019-10-30_14:28:46/extensions/LiquidThreads/classes/Threads.php(157): Threads::where(Array, Array, true) #7 /srv/mediawiki/tags/2019-10-30_14:28:46/extensions/LiquidThreads/api/ApiFeedLQTThreads.php(187): Threads::withRoot(Object(Article)) #8 /srv/mediawiki/tags/2019-10-30_14:28:46/extensions/LiquidThreads/api/ApiFeedLQTThreads.php(58): ApiFeedLQTThreads->getConditions(Array, Object(Wikimedia\\Rdbms\\MaintainableDBConnRef)) #9 /srv/mediawiki/tags/2019-10-30_14:28:46/includes/api/ApiMain.php(1603): ApiFeedLQTThreads->execute() #10 /srv/mediawiki/tags/2019-10-30_14:28:46/includes/api/ApiMain.php(539): ApiMain->executeAction() #11 /srv/mediawiki/tags/2019-10-30_14:28:46/includes/api/ApiMain.php(510): ApiMain->executeActionWithErrorHandling() #12 /srv/mediawiki/tags/2019-10-30_14:28:46/api.php(83): ApiMain->execute() #13 {main} ","exception_id":"aa9df05a8c6ccf5e2e4aca5a","exception_url":"/w/api.php?action=feedthreads&type=replies%7Cnewthreads&thread=Thread%3AUser+talk%3A%E1%83%9B%E1%83%90%E1%83%A0%E1%83%92%E1%83%90%E1%83%9A%E1%83%9D%E1%83%9C%E1%83%90%2FTranslation+request+for+Georgian&feedformat=atom","caught_by":"mwe_handler"} [] [31-Oct-2019 04:18:35 UTC] PHP Notice: Exception doing lazy updates: Exception: synchroniseArticleData called on null article in /srv/mediawiki/tags/2019-10-30_14:28:46/extensions/LiquidThreads/classes/Threads.php:308 Stack trace: #0 /srv/mediawiki/tags/2019-10-30_14:28:46/extensions/LiquidThreads/classes/Thread.php(968): Threads::synchroniseArticleData(NULL, 100, 'cascade') #1 /srv/mediawiki/tags/2019-10-30_14:28:46/extensions/LiquidThreads/classes/Thread.php(591): Thread->doLazyUpdates() #2 /srv/mediawiki/tags/2019-10-30_14:28:46/extensions/LiquidThreads/classes/Thread.php(519): Thread->__construct(Object(stdClass)) #3 /srv/mediawiki/tags/2019-10-30_14:28:46/extensions/LiquidThreads/classes/Thread.php(729): Thread::newFromRow(Object(stdClass)) #4 /srv/mediawiki/tags/2019-10-30_14:28:46/extensions/LiquidThreads/classes/Threads.php(97): Thread::bulkLoad(Array) #5 /srv/mediawiki/tags/2019-10-30_14:28:46/extensions/LiquidThreads/classes/Threads.php(104): Threads::loadFromResult(Object(Wikimedia\Rdbms\ResultWrapper), Object(Wikimedia\Rdbms\Maintainab in /srv/mediawiki/tags/2019-10-30_14:28:46/extensions/LiquidThreads/classes/Thread.php on line 593