After I updated my mediawiki from 1.27 to 1.28 I also updated my extensions to 1.28 stable version along with Flow, and after I run update.php I was getting the an error and my flow boards aren't working anymore(and in a lot of cases I also got a white page with http 500 error where flow boards supposed to be):
```
PHP Notice: Use of undefined constant CONTENT_MODEL_FLOW_BOARD - assumed 'CONTENT_MODEL_FLOW_BOARD' in /var/www/html/LocalSettings.php on line 565
PHP Notice: Use of undefined constant CONTENT_MODEL_FLOW_BOARD - assumed 'CONTENT_MODEL_FLOW_BOARD' in /var/www/html/LocalSettings.php on line 566
```
```
[6e41278a3968bd2cf8dedf04] /User_talk:Innosflew MWUnknownContentModelException from line 347 of /var/www/html/includes/content/ContentHandler.php: The content model 'CONTENT_MODEL_FLOW_BOARD' is not registered on this wiki.
See https://www.mediawiki.org/wiki/Content_handlers to find out which extensions handle this content model.
Backtrace:
#0 /var/www/html/includes/page/WikiPage.php(225): ContentHandler::getForModelID(string)
#1 /var/www/html/includes/page/WikiPage.php(212): WikiPage->getContentHandler()
#2 /var/www/html/includes/actions/Action.php(96): WikiPage->getActionOverrides()
#3 /var/www/html/includes/actions/Action.php(154): Action::factory(string, WikiPage, RequestContext)
#4 /var/www/html/includes/MediaWiki.php(151): Action::getActionName(RequestContext)
#5 /var/www/html/includes/MediaWiki.php(767): MediaWiki->getAction()
#6 /var/www/html/includes/MediaWiki.php(512): MediaWiki->main()
#7 /var/www/html/index.php(43): MediaWiki->run()
#8 {main}
```
Then after this updated my mediawiki to 1.29.0-alpha (5b211eb) version and also my extensions along with the Flow to check if it's working with a newer version but I was still getting the same error. The only way I was able to make Flow working again if I switched back to the 1.27 version of the Flow extension I was using before I updated to 1.28. 1.27 Flow seems it's working with the mediawiki 1.29.0-alpha, the only problem I have is still is that I am only able to use the SourceEditor part of Flow when making posts or comments, I am not able to use the VisualEditor on the Flow boards, because if I click to switching to VisualEditor while I editing my post it starts load infinitely(https://i.gyazo.com/0d59ee299fc1447f245d551e7e4f5aa7.png) and it doesn't load up the VisualEditor.