I cannot log in my own profile

I'm a Chinese firefox user, so the following descriptions are translated and may not be so accurate. And the attached image is also Chinese, if necessary please use a translation app or somewhat to see it. I have only one default profile in my Firefox account, and I have stored a large number of passwords and bookmarks in this default profile. For certain reasons, I signed out of this profile while retaining the local data such as passwords—meaning that, apart from not being logged in, my browser state remains exactly the same as before. Now I wish to sign back in to enable synchronization. I can see a "Sync and Save Data" button prompting me to log in. After clicking this button, I am asked to enter my username and password, but then I receive a message stating that I have reached the account limit for this profile, and that this profile was previously synced to another account. This is absurd, as I do not have another account, nor have I ever synced this profile to any so-called other account. As a result, I am unable to sign in on this current profile.