Question for strange AuthenticatorTransport ( cable , blank )

[taeseon-lee]

hi.
In my case, some strange case exist.

• On Android & FireFox,
  AuthenticatorTransport return cable, internal

• On iCloud keychain(some few strange case)
  AuthenticatorTransport return blank (means empty string)

Any ideas what is going wrong here?
do you have any plan for this case?
or should i filter those strange AuthenticatorTransport case, and revise to other normal value?