In T188180#8117935, @Umherirrender wrote:

$wgAbuseFilterNotifications = 'rc' or 'rcandudp' is broken as well and throws CannotCreateActorException (it's post send, not visible to the wiki), the proposal does not fix that part (because CheckUser would be called from RecentChanges for that configs)

I have also no idea. Creating an hidden/locked account with invalid password/token for this purpose allows to create the actor entry, but could have other issues for oversighters to see this, reporting if someone tries to create such the name a second time or other issues. Using an interwiki user also looks not nice.
Using the ip as actor seems not wanted and is unexpected when a user with AGF is filtered as false positive, if I understand the hint to some private bugs above correctly.