Looking for logging into the Sharepoint Issues site and are not getting the correct working link for it? In such a case, you can use the links given here by searching your desired login page in the search box. If the page is present on our website then you will get all the links related to the Sharepoint Issues site. After that you can login as usual with your login credentials.
https://answers.microsoft.com/en-us/msoffice/forum/msoffice_sharepoint-mso_win10/sharepoint-login-issues-office-365/1feed983-0d6c-4aa7-a468-611d09c9c295
https://www.c5insight.com/Resources/Blog/tabid/148/entryid/275/sharepoint-login-issues-how-to-fix-users-who-cant-log-in-via-their-user-principle-name-upn.aspx
https://kb.intermedia.net/article/3244
https://mso.harvard.edu/news/sharepoint-login-issues
http://downdetector.com/status/office-365
https://community.spiceworks.com/topic/2016469-sharepoint-online-office-login-issues
https://sharepoint.stackexchange.com/questions/227835/login-issue-in-sharepoint-designer-2013
https://blog.kloud.com.au/2017/08/10/sharepoint-online-external-user-access-error-user-not-in-directory/
https://support.realconnections.nl/hc/nl/articles/208151816-Resolve-SharePoint-Designer-connection-issues
https://status.office365.com/
https://www.netwoven.com/2017/05/30/sharepoint-2013-multiple-login-prompt-issue/
https://www.linkedin.com/learning/troubleshooting-microsoft-online-services/common-office-365-sharepoint-problems
https://support.office.com/en-ie/article/error-message-when-an-external-user-accepts-a-sharepoint-online-invitation-by-using-another-account-f0d34413-ea7c-42c7-a485-c4e5d421e5f0