@T_B_ Thank you for reaching out to us. As I understand you would like to investigate about the audit logs having this information 255.255.255.255.
Did a quick repro in my demo tenant, on deleting the authenticator app information from a user within Azure AD portal trigger's below information within the audit logs.
Activity Type - Admin deleted security info
Status reason - Admin deleted Microsoft Authenticator Authentication Method for user
IP address - 255.255.255.255
Just wanted to check are you trying to delete authenticator app information for any user from Azure AD portal? were you able to delete it successfully? Thats when you see this ip address being logged in the Audit logs.
Let me know if you have any further questions, feel free to post back.