Sub-sites details not being removed or updated

We need to change the address of a sub-site from http to https. We have tried disconnecting the http and reconnecting via the new https address, however the old http site remains listed under the master site.

We have also tried manually editing the option value under user_sync_options (changing the sub-site to https), and it records our change, but it is almost instantaneously rewritten back to the old option’s value (with the sub-site as http).

How can we force the plugin to recognise the new address?