Visit a non-existent user_talk page on ee-flow and click the pencil to edit the Flow board header.

You get a pink errorbox:

An error occurred.
The error message received was: Exception Caught: Unable to load topic list history for <UUID>

I'm not sure what <UUID> is, there isn't a UUID yet. I was logged in at the time as Admin.

For a recent failure, the request is

action=query
flowpage=User talk:Gersh
flowparams={"header":{"contentFormat":"wikitext"}}
flowworkflow=
format=json
list=flow

The API response and the debug.log contain:

[exception] [907b0db4] /w/api.php?action=query&format=json&list=flow&flowpage=User+talk%3AGersh&flowworkflow=&flowparams=%7B%22header%22%3A%7B%22contentFormat%22%3A%22wikitext%22%7D%7D Exception from line 84 of /srv/mediawiki/extensions/Flow/includes/Block/BoardHistory.php: Unable to load topic list history for rqgykdahb0eanhv0
#0 /srv/mediawiki/extensions/Flow/includes/Block/BoardHistory.php(65): Flow\Block\BoardHistoryBlock->loadBoardHistory()
#1 /srv/mediawiki/extensions/Flow/includes/api/ApiQueryFlow.php(39): Flow\Block\BoardHistoryBlock->renderAPI(Object(Flow\Templating), Array)
#2 /srv/mediawiki/includes/api/ApiQuery.php(279): ApiQueryFlow->execute()
...

The workaround is to create a first topic (which has its own bug that you can't preview it).

Version: master
Severity: normal