Actually I think the issue is you are trying to use it as a log in.
FB connect has 2 purposes.
Send invites to FB friends and move your account.
FB connect is not used the same way as Google/apple login.
https://help.ea.com/en/help/star-wars/star-wars-galaxy-heroes/how-to-save-your-progress-in-star-wars-galaxy-of-heroes/
Linking to Facebook won’t save your game progress. If you want to send Ally invites to your Facebook friends, connect to Facebook with these steps.
Check
https://help.ea.com/en/help/star-wars/star-wars-galaxy-heroes/self-service-tool-star-wars-galaxy-of-heroes/
Follow the steps under "Move to a device with a different operating system"
Yes I know you are the same os on both but this is the only way to copy one guest account to another.