Change 702707 had a related patch set uploaded (by Reedy; author: Reedy):

[mediawiki/extensions/ConfirmEdit@wmf/1.37.0-wmf.12] Revert "Replace depricating method IContextSource::getWikiPage && IContextSource::canUseWikiPage"

https://gerrit.wikimedia.org/r/702707

Change 702706 had a related patch set uploaded (by Reedy; author: Reedy):

[mediawiki/extensions/ConfirmEdit@master] Revert "Replace depricating method IContextSource::getWikiPage && IContextSource::canUseWikiPage"

https://gerrit.wikimedia.org/r/702706

Change 702707 merged by jenkins-bot:

[mediawiki/extensions/ConfirmEdit@wmf/1.37.0-wmf.12] Revert "Replace depricating method IContextSource::getWikiPage && IContextSource::canUseWikiPage"

https://gerrit.wikimedia.org/r/702707

Mentioned in SAL (#wikimedia-operations) [2021-07-01T16:23:01Z] <reedy@deploy1002> Synchronized php-1.37.0-wmf.12/extensions/ConfirmEdit/SimpleCaptcha/SimpleCaptcha.php: T285959 (duration: 01m 20s)

Change 702706 merged by jenkins-bot:

[mediawiki/extensions/ConfirmEdit@master] Revert "Replace depricating method IContextSource::getWikiPage && IContextSource::canUseWikiPage"

https://gerrit.wikimedia.org/r/702706

Have some investigating there, so when we replace IContextSource::getWikiPage to creating new instance of page in ConfirmEdit extension ( SimpleCaptcha::confirmEditMerged ) in scope of T275710 we broke a logic of activation captcha when we add external link. We set a value to activate captcha $page->ConfirmEdit_ActivateCaptcha = true;
Then in SimpleCaptcha::showEditFormFields we check this variable ConfirmEdit_ActivateCaptcha to add captcha to output if needed. After updates to deprecate IContextSource::getWikiPage and replace it with WikiPageFactory::newFromTitle we create new instance, but used old instance here SimpleCaptcha::showEditFormFields to check the variable ConfirmEdit_ActivateCaptcha. All rules to addurl pass correctly that why we didn't received any errors and only that variable above block adding captcha form to output. The page just reload, as it expect that captcha form will be shown and user will pass captcha to save changes. Probably we can move this variable to hook handler, but better wait till T242249 will be ready so we could have edit state injected through hook handler and can set extension data there to prepare this variable ConfirmEdit_ActivateCaptcha that will be not depend on WikiPage.