the addresses previously entered (prior to linking eM Client) have disappeared in both locations(In Google contacts online and in eM Client.
I would then contact Google support for assistance via posting on their Gmail community forum link below. Or via phone if you have a paid Google One or paid Workspace account.
Adding your Google / Gmail account to eM Client doesn’t remove any contact information from your online account. That only just reads / shows what you already have in your online account
(Post to the Gmail help community)
https://support.google.com/mail/thread/new
I might have the info in an exported csv somewhere.
Yes if you have previously exported your Google contacts with addresses in it to a .CSV file then you can reimport them online. See the following Google support link.
(Import your contacts into Google Contacts)
You can also import .CSV files in eM Client via @Gary post in the following thread.