The cuc_id is 885298421. Error is reproducible at Special:CheckUser by querying for that IP in a date range that includes September 7, 2019.
From /srv/mediawiki/php-1.34.0-wmf.23/extensions/CheckUser/includes/specials/SpecialCheckUser.php:1805
Logstash: https://logstash.wikimedia.org/goto/7feed5976d9b86f6bc909f81b0fe5614
Stack trace:
#0 /srv/mediawiki/php-1.34.0-wmf.23/extensions/CheckUser/includes/specials/SpecialCheckUser.php(946): SpecialCheckUser->CUChangesLine(stdClass) #1 /srv/mediawiki/php-1.34.0-wmf.23/extensions/CheckUser/includes/specials/SpecialCheckUser.php(745): SpecialCheckUser->doIPEditsRequestOutput(Wikimedia\Rdbms\ResultWrapper, string, boolean) #2 /srv/mediawiki/php-1.34.0-wmf.23/extensions/CheckUser/includes/specials/SpecialCheckUser.php(110): SpecialCheckUser->doIPEditsRequest(string, boolean, integer) #3 /srv/mediawiki/php-1.34.0-wmf.23/includes/specialpage/SpecialPage.php(575): SpecialCheckUser->execute(NULL) #4 /srv/mediawiki/php-1.34.0-wmf.23/includes/specialpage/SpecialPageFactory.php(611): SpecialPage->run(NULL) #5 /srv/mediawiki/php-1.34.0-wmf.23/includes/MediaWiki.php(296): MediaWiki\Special\SpecialPageFactory->executePath(Title, RequestContext) #6 /srv/mediawiki/php-1.34.0-wmf.23/includes/MediaWiki.php(892): MediaWiki->performRequest() #7 /srv/mediawiki/php-1.34.0-wmf.23/includes/MediaWiki.php(523): MediaWiki->main() #8 /srv/mediawiki/php-1.34.0-wmf.23/index.php(44): MediaWiki->run() #9 /srv/mediawiki/w/index.php(3): require(string) #10 {main}