When i sign in , i can't access my skin offline. I have to turn on Wi-Fi or choose again same skin.Your skins load infinity in offline.If you don't sign in , you can access your skin easily without internet. Not only custom skins, it also happens with Steve and alex skins. 

Steps to reproduce-:

1) Sign into your microsoft account.

2) Choose any custom skin.

3) Then close your minecraft and open your minecraft again. Remember : Turn off Internet or wi-Fi

4) Check your skin . You can see your see skin load infinitely. Be sure to turn off Wi-Fi or internet before opening minecraft

Observed results-:

1) Your custom skins load up infinitely when you play offline

Expected results-:

2) Your custom skins load even if you sign in without internet.