Just Dance 2019 users experiencing issues with Ubisoft account logins

Just Dance 2019 seems to have some sort of connection issue with Ubisoft accounts, at least on the Switch. Multiple owners are reporting that they cannot link or log into their Ubisoft accounts. Every time they try, they're greeted with an error about the account not being found, or not existing. Some people have gone so far as to create multiple new accounts just to test if the login works that way, and it does not. Ubisoft is yet to comment on this issue.