Iphone 12 Pro, iOS Version 18.1.1
BlueWallet app version: 7.0.7 (build 1736867217 master)
self-test passes: OK

I am able to set a custom preferred server, save it (I get the confirmation dialog and click ok) and connect to it successfully.

When I close the app and return to the Electrum Server settings I see my server in the Status section but the Preferred Server section shows one of the Suggested Servers not my custom preferred server.

If I close the app again and return to the Electrum Server settings I see the one of the Suggested Servers in the Status section instead of my custom preferred server.

This creates operational security concerns.