It is possible that your deploy with fail with no error message after you switched GitHub settings like:
In most cases this can be quickly fixed by visiting https://github.com/settings/installations and removing fleek from the Authorized and Installed tabs. Then simply reinstall fleek on app.fleek.co on the hosting tab, by triggering a new deploy or adding a site.
If the above still didn't solve your issue, please open a support ticket for fleek.co and we will fix this for you. You will need to provide your site's fleek url ( for example, "burning-hall-9201.on.fleek.co" )