I extended the Bootswatch theme into a custom theme but found token.twig was not included in the theme editor. I was able to work around this issue by copying the /logincomponents folder from the Vanilla theme to the Bootswatch theme, then modifying the config.xml (<welcome> node) to include both the token.twig and the captcha.twig files in that folder.

The issue was reported here along with details: https://www.limesurvey.org/forum/design-issues/118139-token-page-custom-text

Based on DenisChenu's reply, I'm reporting it here for a complete fix.