Keys and addresses
An onion address is derived from a cryptographic key. If the key is replaced, the address changes with it.
Planned rotation
Operators sometimes rotate addresses to shed traffic floods or to move to new infrastructure.
Unplanned changes
A suspected key compromise forces an immediate change. These are the moments when fake announcements multiply.
What stays the same
Your account and login stay the same across a genuine change; only the address in the bar is different.
A genuine WeTheNorth address change never changes your account, only the address you reach it through.