This appears to mainly be happening to testwiki on snapshot1006, but it's a little noisy in the logs. Seems like this was a problem in both 1.30.0-wmf.1 and 1.30.0-wmf.2, but I noticed it deploying 1.30.0-wmf.2 to group0 today.
Flow\Exception\InvalidDataException from line 366 of /srv/mediawiki/php-1.30.0-wmf.2/extensions/Flow/includes/Model/AbstractRevision.php: Failed to load the content
#0 /srv/mediawiki/php-1.30.0-wmf.2/extensions/Flow/includes/Dump/Exporter.php(419): Flow\Model\AbstractRevision->getContent(string)
#1 /srv/mediawiki/php-1.30.0-wmf.2/extensions/Flow/includes/Dump/Exporter.php(336): Flow\Dump\Exporter->formatRevision(Flow\Model\PostRevision)
#2 /srv/mediawiki/php-1.30.0-wmf.2/extensions/Flow/includes/Dump/Exporter.php(263): Flow\Dump\Exporter->formatRevisions(Flow\Model\PostRevision)
#3 /srv/mediawiki/php-1.30.0-wmf.2/extensions/Flow/includes/Dump/Exporter.php(221): Flow\Dump\Exporter->formatPost(Flow\Model\PostRevision)
#4 /srv/mediawiki/php-1.30.0-wmf.2/extensions/Flow/includes/Dump/Exporter.php(204): Flow\Dump\Exporter->formatTopic(Flow\Model\PostRevision)
#5 /srv/mediawiki/php-1.30.0-wmf.2/extensions/Flow/includes/Dump/Exporter.php(182): Flow\Dump\Exporter->formatWorkflow(Flow\Model\Workflow, Flow\Search\Iterators\HeaderIterator, Flow\Search\Iterators\TopicIterator)
#6 /srv/mediawiki/php-1.30.0-wmf.2/extensions/Flow/maintenance/dumpBackup.php(86): Flow\Dump\Exporter->dump(BatchRowIterator)
#7 /srv/mediawiki/php-1.30.0-wmf.2/extensions/Flow/maintenance/dumpBackup.php(57): FlowDumpBackup->dump(integer)
#8 /srv/mediawiki/php-1.30.0-wmf.2/maintenance/doMaintenance.php(111): FlowDumpBackup->execute()
#9 /srv/mediawiki/php-1.30.0-wmf.2/extensions/Flow/maintenance/dumpBackup.php(125): require_once(string)
#10 /srv/mediawiki/multiversion/MWScript.php(99): require_once(string)
#11 {main}