After this update, when editing clients none of the previously selected servers show for Web/Email/XMPP/Database. The selected nameserver does display. I can select servers again and hit save, there are no errors, but when editing the client again those fields are empty.

The same fields are fine for a reseller, ie. they show the correct/previously saved servers.

Ok, so the reseller is still broken. The behaviour that you describe for the client is the intended behaviour, as manually selected servers have to be replaced by the ones that are selected in the templates. Edit the templates and select the desired servers, you will see that they get applied to the client then when you edit and save the client.