I got 2 replies which didn't convinced me much:
We are so sorry for any inconvenience caused. I totally understand your concern. To protect account security, customers will receive notifications if their accounts were login other device. But we noticed that sometimes customers still receive noticitation even their accounts were never login other devices. In this case, the notification is not accurate. Our engineers are looking into this issue and ensure you that this issue will be resolved soon.
Asked to escalate the issue and got this:
I double checked the issue with our engineers. If the app hasn't been login more than 30 days, customers will receive this notification. But I'm so sorry that the words in the notification are not accurate. We just want to remind customer to change password to protect account security as their accounts haven't been login for a long time. We will improve the language as soon as possible.
Which also doesn't make a lot of sense since I've been using the app everyday.
Will update when I have more replies from anker