Check your current external IP first. This can be done, for example, here or here... Compare the received address with the one indicated in the letter and with those that are displayed in authorizations report... If the address matches, then the reason for the trigger could be the change of IP on the device from which the account was previously logged in. This situation can arise when the IP provider changes its IP, connects to the network of another provider, or, for example, when you turn on a proxy or VPN.
If you suspect that someone else may have gained access to your account, you should take appropriate action: