The error message is:

PHP fatal error in /srv/mediawiki/php-1.24wmf20/extensions/GeoCrumbs/GeoCrumbs.class.php line 126:
Call to a member function getProperty() on a non-object

getParserCache() can return null, but the code doesn't handle this situation, assuming it will never return null.

Change 160306 had a related patch set uploaded by Florianschmidtwelzow:
Handle return value NULL of GeoCrumbs::getParserCache

https://gerrit.wikimedia.org/r/160306

Change 160306 merged by jenkins-bot:
Handle return value NULL of GeoCrumbs::getParserCache

https://gerrit.wikimedia.org/r/160306

Change 160388 had a related patch set uploaded by Florianschmidtwelzow:
Handle return value NULL of GeoCrumbs::getParserCache

https://gerrit.wikimedia.org/r/160388

Change 160389 had a related patch set uploaded by Florianschmidtwelzow:
Handle return value NULL of GeoCrumbs::getParserCache

https://gerrit.wikimedia.org/r/160389

Change 160389 merged by jenkins-bot:
Handle return value NULL of GeoCrumbs::getParserCache

https://gerrit.wikimedia.org/r/160389

Change 160388 merged by jenkins-bot:
Handle return value NULL of GeoCrumbs::getParserCache

https://gerrit.wikimedia.org/r/160388

Patches merged to 1.24wmf21, 1.24wmf20 and master. Thanks! Closing as FIXED.

And deployed to wikivoyage :)