If names on your contacts — or on contracts — change without anyone in your agency touching them, this is the contact sync doing exactly what it's built to do. Contacts sync both ways between Gigwell and your agency's linked Google account, and the return direction can't be switched off.
Why it happens
Your contacts really live in the linked Google account. Anything else connected to that same Google account can edit those records, and those edits come back into Gigwell. In practice the culprit is nearly always one of these:
A phone address book synced to the linked Google account.
A messaging or contacts app signed in to that account, tidying or auto-merging entries.
A second person working in Google Contacts directly.
What to do
List every device and app signed in to your agency's linked Google account. You can check which account that is at Settings > Calendar & Templates > Calendars.
Turn off contact syncing for that account on personal phones, and disconnect messaging or contact-cleanup apps from it.
Treat the linked Google account as agency infrastructure — it isn't a good account to sign in to on a personal device.
When a lineup needs to change on a booking, swap the artist from the booking's Change tab rather than editing a contact card. Editing the card doesn't do what people expect.
If you need to actually change a contact's name or email
Editing a contact inline in Gigwell only updates the mapped Google Contact — the Gigwell record stays as it was, which is why the old value reappears. There's a specific revert-and-recreate procedure that makes the change stick, and it's covered in the articles on changing a contact's name or email and changing an artist's name. Follow those rather than editing the card in place.
If that doesn't work
If your contact list simply looks stale or out of date, refresh it: go to Contacts, open Manage Settings, and choose Clear Cache. That reloads the list without changing any data.
If a contact stays stuck to the wrong Google record after all of the above, that mapping has to be cleared for you — start a chat from the messenger and we'll get it sorted.
Good to know
There's no outbound-only mode for contacts, so controlling what's connected to the linked Google account is the real fix. Calendars behave differently: bookings push out to Google one way only, and nothing you do in Google Calendar edits a booking.