Sorry to bother...but the same problem occurred again.

No problem, thank you for re-opening and letting us know about the issue, I'm sorry it's not sorted out yet. We want to get it fixed! :)

鱼头炮 said he clicked the "disable structured discussions board" button and saved changes in "preference", and 'Fatal exception of type "Flow\Exception\InvalidDataException" ' error appeared again.

My suspicion (noted in T70526#4531691) was that the Flow talk manager bot failed to move flow boards for users whose talk pages were protected. However as far as I can tell, 鱼头炮's talk page is not protected, so it's unclear to me what's happening here.

In the logs, I see that an exception is thrown by Flow's OptInController and the message in the log contains the text:

'''You can't currently edit Wikipedia'''
'''You can browse the page ''' but can't edit, move or create a page

This shouldn't be a problem, though, because it's supposed to be Flow talk manager bot that archives the flow board and moves the old talk page back into place. And in theory, if a failure like this occurs, Flow is supposed to roll the Flow and Mediawiki DB back to a known good state but that doesn't appear to be working properly.

I'll keep looking into it and let you know what I can figure out.

Note that the log message you're talking about begins with {| id="mw-blocked-text" . It looks like this is https://zh.wikipedia.org/w/index.php?title=MediaWiki:Blockedtext&action=edit . So there's definitely a failure related to a user being blocked.

The backtrace is:

#0 /srv/mediawiki/php-1.32.0-wmf.18/extensions/Flow/includes/Import/OptInController.php(550): Flow\Import\OptInController->fatal(Message)
#1 /srv/mediawiki/php-1.32.0-wmf.18/extensions/Flow/includes/Import/OptInController.php(680): Flow\Import\OptInController->editBoardDescription(Title, Closure$Flow\Import\OptInController::archiveFlowBoard;4169, string)
#2 /srv/mediawiki/php-1.32.0-wmf.18/extensions/Flow/includes/Import/OptInController.php(183): Flow\Import\OptInController->archiveFlowBoard(Title)
#3 /srv/mediawiki/php-1.32.0-wmf.18/extensions/Flow/includes/Import/OptInController.php(119): Flow\Import\OptInController->disable(Title)
#4 /srv/mediawiki/php-1.32.0-wmf.18/includes/deferred/MWCallableUpdate.php(34): Closure$Flow\Import\OptInController::initiateChange()
#5 /srv/mediawiki/php-1.32.0-wmf.18/includes/deferred/DeferredUpdates.php(268): MWCallableUpdate->doUpdate()
#6 /srv/mediawiki/php-1.32.0-wmf.18/includes/deferred/DeferredUpdates.php(214): DeferredUpdates::runUpdate(MWCallableUpdate, Wikimedia\Rdbms\LBFactoryMulti, string, integer)
#7 /srv/mediawiki/php-1.32.0-wmf.18/includes/deferred/DeferredUpdates.php(134): DeferredUpdates::execute(array, string, integer)
#8 /srv/mediawiki/php-1.32.0-wmf.18/includes/MediaWiki.php(914): DeferredUpdates::doUpdates(string)
#9 /srv/mediawiki/php-1.32.0-wmf.18/includes/MediaWiki.php(734): MediaWiki->restInPeace(string, boolean)
#10 [internal function]: Closure$MediaWiki::doPostOutputShutdown()
#11 {main}

I'm not sure why this happens though, because editBoardDescription() passes in a RequestContext that has been modified (by the OptInController constructor) to have the user set to the Flow talk page manager user rather than the talk page's owner, and as far as I can tell this seems to be propagated correctly by the rest of the code. The source of the blocked message appears to be line 88 of SubmissionHandler.php, which is not at all deep in the call stack from editBoardDescription.

@Cosine02 sorry for the slow progress on this one. It has been quite difficult to track down, as we cannot reproduce it in our development environments. I've added some logging statements, so the next time 鱼头炮 tries to disable structured discussions we should have some more information to help debug.